I know this is quite popular from the Wii and PS3 experience ... but what about big products like gBuy? Anyone pick up domain names associated with these big internet applications, paypal, gbuy, etc.?
I highly do not recommend to get a domain name with gBuy in it. Google will snatch it from you. But some companies dont really push the issue but all the ones you listed do.
Well only reason I asked is that I snatched up gwallet.org today and just ran a trademark search and it's not a trademarked name so I don't see any complications. worst comes to worst I'd get issued a C&D, but I don't see why that'd happen.
The US has "common law" trademarks - so a person does NOT need to get a Federal Trademark to own the rights to it - they only need to be the first one to use it, and continue to use it (the different domain extension doesn't matter). I'm not commenting on the specific domain you mentioned, just the method you used. The USPTO is only one place you should check. You can always run a check on google for a name as a quick check to see if it is already being used, but a full trademark search starts at a few hundred dollars - and even that isn't a 100% guarantee that you won't have infringement problems down the road.
From what I've heard Google is pretty aggressive at going after anything they consider an infringement.