I donated a few times in the past because I really wanted
Thanks.
but others (who could easily afford it) might not even think of that just because they are not asked (that's just human psychology). So, please ask more!
Based on the donation statistics of other projects, I think donate buttons tend to do more harm than good because 99% of visitors have no intention of donating (and I don't blame them) -- so to them, the button is just a nag or distraction. Also, the site has been given free hosting by Aybra, which helps too.
If you don't want/need the money, I suggest you find some awesome, trustworthy coder at a site like http://www.rentacoder.com/ and pay him/her to optimize the code and/or to improve certain features.
I doubt a donate button would collect enough to fund a significant amount of development time unless a single donor gave a large sum, which is unlikely. I think it would be far more valuable to have another developer voluntarily join the project.
This is not to say there will never be a donate button. But as long as the project/site doesn't need the money, I'd prefer not to have one.
Thanks.