Well, for a number of people, the last stage is Death by Mod. They decide they’re done here and decide to go out in a blaze of idiotic glory.
Most of us, though, seem to settle into a quiet “who the hell is that poster, he seems familiar” occasional contribution to the occasional thread.
For me it was General Questions and Cafe Society, and of course Comments on Cecil’s Columns/Staff Reports. None of the other forums interested me. As I got more familiar with the regulars around here, I began venturing into IMHO and MPSIMS. I’ll occasionally dip a toe into The Game Room, but I never stay for long. Still don’t venture elsewhere very often.
**Stage 1: Lurking ** – I don’t think I ever lurked. I honestly can no longer remember how/why I came here, but I’m pretty sure my aim was to participate right away. I’d been on a couple of other message boards, so while I don’t think I was actively looking for a new one I was already comfortable with the idea of posting.
Stage 2: MPSMIMS/IMHO Only – Add the other “safe” forums – Cafe Society, ATMB, and GQ – and that was me. 
Stage 3: The Rest of the Board – I eventually ventured into the Pit, but I have deliberately never visited GD. My experience on other boards taught me that debates get me in trouble (never banned, but worked up enough to quit), so I decided to avoid them entirely here. So far, so good!
Stage 4: Regretting My User Name – I <3 my user name. I was very, very lucky (and a bit surprised) that it was available when I registered.
Stage 5: Using Dope Slang IRL – OMG all the time. Luckily, mostly the only one who ever hears it is my dog. I hear Dope slang commentary in my head a lot, though (e.g., someone leaves a room and says “I’ll be back,” and in my head I hear “when come back, bring pie!”).
A stage I will add is Hardly Ever Starting Threads Anymore Because You Don’t Want to Deal With the Literalist Judgmental Bullshit. It started with learning not to start Pit threads, because no matter what you’re complaining about or how justified you are unless you word your post perfectly and include every possible detail some asshole will do a drive-by and either pick apart everything you wrote or assume they know way more about your situation than you do. Or both. That lesson quickly spread to IMHO and MPSIMS posts, too, unless I’m asking for opinions. No more posts that are just venting, looking for support, etc. There are a lot of awesome people here, but there are also a lot of dicks who like to pretend they have no idea what you’re talking about. Wading through those responses just isn’t worth it anymore.
2 Stages that I went through include:
X: Think that referencing a board meme makes me cool (e.g. Hi Opal).
X+1: Realize that referencing a board meme does not make me cool. (i.e. Bye Opal).
Oh god, yes. I started a thread once asking if all Spanish speakers can understand each other, giving as an example my attempts to watch some films from the UK where I struggled to understand some accents.
Someone demanded to know why I was claiming not to understand James Bond movies.
Stage 1a: Start IRL conversations with, “I was reading this thread on the Straight Dope Message Board…”
Stage 1b: Realize that no one else IRL cares about what you read on the SDMB. Sob quietly to yourself. Console yourself by reading some more SDMB.
I’m very active on a couple of boards. When I share something from *this *board IRL, I always start with “Today on the smart board…”
True. Congratulate yourselves. 
I’m new to this weird and wonderful world, at less than a year. I came in with the shopping channel snarkers at the time of The Great Upheaval. I lurked for about 3 days, I think, then decided y’all had a right to my opinion on things, so I started giving it.
I’m not fully in with the in crowd, but I decided I was making progress toward it when I:
a. Started ticking people off and getting my stuff handed to me most righteously.
b. Had the cojones to start a pit thread on a very controversial topic and didn’t let the howling rabble scare me away. In fact, I found it exhilarating and stayed in there slugging.
Now, after b above, you’re stuck with me. I’ll never leave.
I left out a stage… it’s the one where you have an opinion on everything and HAVE to share.
Then, mercifully, you get to the place where you still have an opinion on everything but “Eh…whatever” <shrug>
I like grapes.
Stage 6: Stop telling medical anecdotes because when I do, I get accused of HIPAA violations (often by people who spell it ‘HIPPA’).
The OP’s list runs similar to my path to enlightenment although I had a stage 0 which was reading the books ( you kids out there might not have heard of this form of media ) in the mid-80’s. Internet access was mostly non-existent where I worked during the AOL days so I was not a lurker until 2000-ish before becoming a member in 2003. I would say I am at Stage 3.
It is a great site and I look at most of the forums every day. I have made it past the 1000 post mark and avoided sanctioned by a mod or being abused in Pit, although I did receive a rebuke from a poster for what they felt was an insensitive post.
Heh…one of my college buddies sent me a newspaper article from her Chicago newspaper–This one, in fact (gawd I love the internet!). That led me to the bookstore where I eventually ended up with The Straight Dope, The Straight Dope Tells All, Return of The Straight Dope, and Triumph of The Straight Dope. Also Extraordinary Origins of Everyday Things (not a Cecil book). The meat people in my life think I’m some kind of genius now because I know a lot of little things, all due to these 8 inches of paperbacks.
I still have a well-thumbed copy of “More of the Straight Dope” published in 1988 with the forward written by Ed Zotti and skillfully illustrated by Slug Signorino. The first story answers the burning question Did Brontosaurs have their brain in their butt ?
Good stuff…
Stage 10: angry rant as attempt at Suicide by Mod.
Stage 11: denial you ever posted on SDMB.
Stage 12: heat death of the universe.
Huh, all this time I thought you had violated a hippo. I am no longer impressed.
Stage 42: drive by commenting.
not me, you…
humor is all left, eh?
Yep. Stage 42. You drop by every few months and every topic has seemingly been done endlessly and and you can’t bother with any drama, so you say hello and leave again.
Proudly lurking for the century, so far…
You forgot the substages to Stage 5:
5a. Recognizing and making SDMB in-jokes like penis ensued, the goat and the squid, and Hi, Opal. And references to the inadvisability of starting threads on cat declawing, tipping, and planes on treadmills.
5b. Realizing that those jokes have run their course and using them makes you seem like you’re trying to show how cool and hip and in the know you are, just to impress the cool kids.