First of all, I'm really thrilled to see that the Soulseek team is bringing SoulSeek to the Mac (and I will donate, for sure). I, and almost every other Mac/Soulseek user, have been waiting for a decent Mac client for ages. The latest nightly build is really showing it's working and on it's way to a really nice piece of software.
But there is one thing I really would love to see changed: the User Interface. It's really not Mac friendly and the navigation is just not done right. There is actually a great example of a really slick UI. Some time ago, there was a project bringing SoulSeek to the Mac, it's called SolarSeek. Later, it became iSoul and now the development of that project died.
The UI was awesome. Check it out at http://code.google.com/p/solarseek/wiki/SolarSeekLayoutScreenshots. I hope to see a more Mac friendly UI in the near future. It would really help making it easy to use and get more Mac users using it.