Key disclaimer though, is that only 95% of donations for tips go to the coders. And if every commit donates 1% of the balance to the commit, that means that the project almost never donates it's full balance. So if this ever really takes off, the original developer of tip4commit will be holding a lot of money that takes a long time to pay out.
We made this project as a part of Rails Rumble contest and are using a limited-time free server offered by them.
So we need to collect money to move to a new server, to cover transaction fees and to continue development of this service if it is demanded.
Maybe we should remove the fees, go opensource and crowdfund ourselves. We were discussing it but haven't made such decision yet.
We don't expect to hold large amounts for a long time because large amounts should attract dozens of commits every day (and thus will turn into small amounts quickly).
If it doesn't happen then we will probably introduce a fixed minimum size for a tip or some other mechanism to solve this problem.
Probably it is good to hold money for some time and to smooth the tip rewards thus placing authors of commits into nearly equal position.
Alternatively, if you do make your site open (and that'd be awesome, please do), you should prominently encourage people to post tips to your repository.