Hmm my reasons for supporting PokeCommunity is the same as it was for supporting Bulbagarden in that my own forum (the forum I would consider home in other words) TPM in 2003 or so, was going through financial difficulties and at the time due to my financial situation I was not able to support them.
Fortunately, I am now in a better financial situation and after being away from the internet literally for four years (no internet at home thus very rarely visited anything outside tpm and one or two other sites), I found myself with the internet again. I feel comfortable within the pokemon community and thus it was natural that with the internet at home again I would choose to visit pokemon sites and forums. And while I don't think I've found exactly what I want. This because TPM is well dying and PC, SPP and BMG just don't feel like a home for me (thats not saying the other communities are bad or anything but I guess I'm just too used to the past etc).
Nonetheless, I first noticed that BMG needed help and thus decided to donate there and even though I saw the donations thing, I didn't think that much of it. But I have been noticing PC being a bit slow at times and I was just browsing the board when I happened to see the donating thread in the announcements forum and decided to donate.
Thus my main reason is to give back to the pokemon community and to try and make up for not at the time being able to help TPM. However, obviously being purple looks great and extra benefits such as a bigger avatar, more pm space and of course secret forums is always a good thing. And it may well compel me to post a bit more round here.
(And I type something that could have easily been said in one or two sentences, lol).