A few years I think… I had another screen name that escapes memory.
I’ve been gone three years.
I came back because I thought it would be dickish to come back only when free posting started.
Depends on how you define “self-imposed ban.” I have been away for 3-6 months at a time (not sure what my record is) due to uproar in my personal life of various kinds (international moving, family illness, insane work/travel schedule) that made it physically impossible for me to check the boards very often - and if I know I won’t be able to stick with an interesting thread, I don’t even look at the SDMB in the first place. So that’s kind of a combination of and internally/externally imposed ban.
Purely voluntary ban, based on having continuous access but wanting to stay away from something rather time-consuming and addictive? Maybe a week or so at a time.
I got angry with an unjustified ( in my view) warning from a mod once and stayed away for a few months. I still get annoyed and maybe stay away for a few weeks at a time.
About 5 years - I was going by the name of blue poop at the time. I used to have some good banter with bippy the beardless (Gosh I miss him!). From what I can remember the board changed and I got frustrated that I was unable to post. I then recently decided to have a look and see how the board was running now. I joined as a guest and my ‘trial’ is soon to end unfortunately as my uni fees are due I will be taking another break from the boards. I’ll miss it here!
I was away for almost 2 years.
I did sign on long enough to renew my membership though – I cherished being a Charter Member even though I didn’t have the time, energy or patience to read the boards, never mind actually post on them.
I’ve been back for a year or so now, not that anyone’s noticed one way or the other 
Well, no offense, but you’re probably going to get banned unless you contact a mod and work out your new screen name. They like it if you stick with your original screen name or formally request a change.
Since you openly admitted your old screen name it’s not like you’re a malicious sock or anything, but they’re still sticklers about that around here.
Not really a ban, but every once in awhile I look through the threads and realize none of them really interest me, or I am not in the mood, or whatever - and just not post for a few days/weeks. With teaching school, sometimes I will go for three or four days and not even check in to read.
Years ago, I remember one Doper was leaving the board and said he had no real gripe or complaint, but that after a time, all the threads seemed to repeat themselves in slightly new variations of the same theme - and he was just tired of it all.
I think he had a point. Sometimes I look at the thread titles and think, “Do I really want to take the time to post the same answer I have posted to similar threads about 60 times over the past years?” That is sort of how my Las Vegas website came to happen…sorta got tired of posting the same info over and over and over again and decided to just write it down and link to it!