I have a dead Serebii account. I don't even remember what username or password I used, or even when I registered. I've also got an EGC account which I haven't signed into for God knows how long, as well as a Castelia City Forums account, which has also perished. If Neoseeker counts as a Pokemon forum, I've also got an account or two there, but again, both of them are deader than the dodo.
The two Pokemon forums where I'm not completely dead are PokeCommunity (duh) and Smogon, which is my main forum so to speak; I've been on Smogon since September 2011 and not about to leave anytime soon. I'm badged there, which means I have Community Member status and can do things most users can't. The one achievement that's given me that privilege is my frequently mentioned modship of their Pokemon Showdown server. I'm much more active there than I am here, although I'll probably step up my PokeCommunity activity at some point.
I've been on several other Poke forums, most notably Neoseeker for General Pokemon (Where I'm still active) and Serebii (Where I'm not active, but have checked occasionally to see some stupid guy who wants to friend me). Then there's that dreaded Gamefaqs *Shivers*... Worst place in the world for forums.
I'm on a lot of Pokémon forums. On BMGf, I go by Veronica. I use the account mostly to lurk. On Serebii, my name is Versus Terminus, and I use it for the same reason as BMGf. I've signed up as CursedWithin on Smogon, but never really logged back into it after my first day there. On PE2K (now known as Pokémon Crossroads), my name is Arch Enemy. This is the place that I'm mostly active in. I grew up there, so it's very hard for me to just abandon it. xD"
I created a bulbagarden account to make edits, not necessarily post in the forums.
I have a smogon account, but I don't like competitive that much, so I don't feel the need to socialize there.
I never even heard of EGC before now, haha. Fail on my behalf.
I used to be active around here, but now I mostly go on EGC. I have an account on a handful of other forums but I rarely visit them. Being on PC and Ever Grande has definitely matured me in many different ways, and browsing them is something I always look forward to doing!