Some Dopers whose tags I need a score-card to tell apart:
bibliophage and bibliophile.
UncleBill and UncleBeer.
asterion and astorian.
I would probably have trouble telling Daniel from Danimal if I didn’t happen to be Danimal. Lucky me.
Anybody else have trouble telling two Dopers’ tags apart?
I sometimes see a post from Kal and wonder “When did I post that?” Does that count?
And then there’s Kaf, just to make things interesting.
I get yojimbo and kwijibo confused.
And I won’t even start on the SDMB/LJ confusions I run into.
Ooh, another episode of doper mixups! I get so very many mixed up…
Super Gnat and Soup_du_jour, Lissa and Lissla Lissar (and sometimes also Lsura), Kal and Kat, and I know there’s many more.
Oh, yes. I spent a few days wondering “Is that other person that I confuse with myself “Kal” or “Kaf”?” before realizing it was both!!
I always confuse Kal and Kaf and myself.
I’m number two for UncleBill and UncleBeer. My apologies to either of you, depending on how you look at it. 
And ChiefScott for ChefTroy.
Tripler
Simple minds are easily confused.
I sometimes confuse CRorex and Cuckoorex. But only in the mornings before I’ve had my coffee.
I get spooje and SPOOFE mixed up a lot.
I have often wondered why it sometimes says “moderator” under UncleBeer and sometimes not. I think I’ve been confusing him with UncleBill.
Weird.
Jomo Mojo, MojoJojo, Mojo & Jojo. Gah! Who’s who? How’s how? Who’s how? How’s who? I have no clue.
I often get myself confused with UnwrittenNocturne
Similar problem for me too, obviously. Also Kali, Kalhoun and Kalessa.
Kallessa, even.
Me and jjtm (who eventually became Troy McLure).
And Malacandra and someone else with a name a bit like Malacandra.
There’s also a bibliovore, as if the first two weren’t enough.
And I always used to mix up Fenris and Feynn.
lee, lel and lieu all fall into the confusion category at times along with Jinx and Janx.
And there’s this Ino guy running around who gets all my credit, too.
jarbaby and jayjay
blanx and blinx
Even though I am blanx, it still makes me doubletake- I don’t remember saying some of that stuff…
I may be mistaken, and this actually may be ONE poster, but I think I have seen both symbalene and synchrolycene (neither one of which I probably spelled correctly.)