Please fix up the UI.

Change the logo, it looks sloppy and unprofessional. If you can't emulate the Twitter logo, then keep it simple and blocky.

Use less of the green. On the start home page, keep only the search box inside of the green and move the tips up and out of it. Don't underline TweepSearch in the header. The tag line is too big make it smaller. In fact do that and replace the logo and it will be a lot better.

The search results are hard to read because they are so long. I read to the end of the line and then I need to scan back carefully to remember who I was looking at. Twitter has a great pattern for short blocks of text. Copy it.

Put more space between search results.

I don't need 25 results per page. 10-15 is okay and you will use less bandwidth in the end.

Save the good for last.
Black, grey, white, and green are good but play around with alternate shades of green.

Round corners are good.

Narrow down the center is also good.

About and Help placed well.

Footer is good.

Donate button stands out and gets your attention, mostly because it is kinda ugly but keep it that way and I think people will look at it.