I take issue with the anonymous "tip" format. I would always prefer a short, personal email -- to me, this is much more meaningful and reflective of why I do open-source. I also think that offering monetary tips encourages tip grubbing. I've already seen a bit of this from big names in the community and, for me, its a big turnoff. I give my code away, that's what OSS is all about. Thank me by writing an email, or better yet, contributing some patches!
As mentioned on your blog, you might be interested in this ticket:
https://github.com/whit537/www.gittip.com/issues/165
The idea is to expand Gittip to encompass other ways of communicating appreciation.
The point is not that people are receiving market rate for services rendered. It is a way to thank, and perhaps motivate individuals by showing an appreciation that is material beyond a simple thank you email.
Many of these people work on free software in their free time; free software that sometimes saves other individuals many hours of work. So what if all I'm doing is buying the person lunch? That is a generous expression and one that builds community and creates emotional and social incentives for the recipient.