I´m running a Roku M1001 and Pinnacle Soundbridge radio, both from an NSLU2 running unslung 6.8 (thrid party firmware), and using the latest Firefly nightly to serve the music. As the previous poster said, the Pinnacle products don´t support DAAP but as long as you go with Firefly this won´t be an issue.
The performance of the units is great and despite having a music library of 10,000+ tracks the NSLU2 manages to survive scanning all of these and serving up the information. This can be a bit slow when you first turn the system on but that is due to the large catalogue of music and with a smaller library would be much faster. I almost never have problems with playback and the few times issues have arisen it has always been a networking problem and never a Soundbridge/NSLU2 issue.
In all I have found the Soundbridge/NSLU2/Firefly to be a fairly bullet-proof setup. SUre the NSLU2 would be a lot happier with a bit more processor power and memory but as long as you aren´t looking to catalogue and play 10´s of thousands of tracks it does a great job.
The only recommendation I would make if you are new to Firefly and the NSLU2 is to start with the latest stable release. The latest nightly, although more feature rich, has a few problems with the dtatbase and scanning during playback. Get your system up and running and enjoy the music before your break it with a nightly release and start pulling your hair out.