I wish /u/changetip all the best, but they have a serious uphill battle to fight. First of all, it is troublesome to have a different tipping mechanism for each and every website where you can use the service.

"I'm on Youtube now and want to send a tip. Do I enter it like I would @twitter or am I supposed to use the +Google symbol?"

Then there is the even much worse problem of never having a clue how much you have left in your changetip account.

"Okay, I think that Youtube is owned by Google and so the + symbol is probably the right one. Now, should I send a cookie or a beer as a tip? I have somewhere around 2-4 dollars in my account but I'd have to go log in just to find out. I just want to watch videos and tip without having to go through all of this!"

Two huge pains for end users.