I've modded a few of them and here are my suggestions:
1) The space for the power supply resevoir cap is tight. If you're going to add one to the board, you have a few options. The first is to use the "tall" version of the 16V/680uF panasonic FC/FM caps over at digikey. These will fit in the stock location between the inductors with no mods. The second method is to skin the inductors. This will let you put a slightly larger (standard sized 680uF-1000uF Panasonic FM/FC) cap in it's place. The third method is to remove this cap altogether and solder it directly to the groundplane and power supply pins on the board. The fourth is to use a cap with the same pin spacing, or with creative lead bending, and place it on the bottom of the board.
2) To get the "best" out of the amp, you need to replace the input coupling capacitor. There's several opinions on this. If you can go with a 2.2uF non-polar black gate (N or NX), this should fit on the pins easily. Another option is stacking 2x 1uF SMD film caps, but this is more difficult. A third option is to dump the whole input filtering section and rebuild it off board. This involves removing jumpering a lot of components and doesn't really provide that much benefit.
I recommend going with a 2.0 to 2.2uF cap, as some folks have reported some nasty startup noises when the chip polarizes caps larger than 2.2uF. Going any larger than 4.7uF seemed to lead to MAJOR noises on start up and shut down. Your mileage may vary, as this seems to depend on the sensitivity of your speakers.
3) Replace the feedback resistors. This is easy. Swap the stock 33/36k (can't remember which it is) resistor for a 20k. This sets the amp to unity gain, and is supposedly the "optimized" configuration in the Tripath datasheet.
4) I've been using 10k Noble pots (the black metal bodied ones that look like Alps "blue velvets"). These work fine. They're not really easily available anymore, though -- I found mine on ebay. Replacing it with a 50k alps, such as the one from tangent's shop, should work fine as well.
Anyhow, be careful as these boards are very cheaply made. It's very easy to lift the pads. There's extensive threads in the diyaudio.com class-d forum on mods for these, including a list of the onboard parts and suggested replacements (posted by myself and panomaniac). You can take these further than what I've posted here (including replacing the output inductors), but you start running into the law of diminishing returns.
The mods I've listed here are what I feel offer the best balance of performance and price. This is a $20-25 amp, so putting $100+ worth of parts, plus all the time and effort, doesn't seem worth it to me. If you really feel like making something better, start with a better platform -- look at the amp3 from
http://www.41hz.com