Well, since you are talking about my abomination, I thought I'll jump in.
First thing of all, sorry for not updating the list, let's just say I'm lazy, and I'll do it today.
Other thing, @Himmat, I don't think I aim for the same userbase; I aim for stats and achievements maniacs like me, and taking care of all the services at once is pretty hard. I want cross platform achievement tracking, with automatic sync for Steam, XBL, and PSN, manual for some PC and Android/iOS games. This is a huge challenge, and I'm still thinking if I should look for people to help with achievement lists and images and stuff. I'm scared that this project just won't work, and I'm going to waste time of many people. We can safely say that I won't be able to add all the games that will come out, and if I will ask for help, I would need to manually verify those lists and stuff, or find people to verify them, which brings us into infinite loop.
I hope that I'm going to figure something out, because this clearly isn't working. Also, Google didn't make a public API or anything, so I can't scrape data from them either. Same with Game Center. Finding high-res images often needed messing around with WireShark or unpacking each .apk and finding them. I even got a installation of Mac OS X for this. Anyways, ranting.
Also, @Twinkling82, I can't assure you can trust me, and I won't even try. You would need to see by yourself. I would say Steam gives the least info about you, and I store only SteamID64 from it. Facebook is next, with profile ID, and Google gives auth token, which I don't know, but I doubt can be used for bad things.
I'm writing this chaos on mobile, I don't see any lines except for last four, so I have no idea what I wrote.
Also, @ExtremeT, fix Google login infinite loop. It's driving me crazy.