Brent:
Been using radioshift for about a year and never had that sort of problem. Did you have the "Radioshift Helper" installed? (thats the background capture tool)
I have had several crashes over the past year but that doesn't sound the same as you,
and today I discovered that Radioshift wasn't deleting old content
that I had deleted (i found my music folder had a radioshift folder full of subscription content that I thought was gone, because I deleted the file from within radioshift) but that wouldn't explain your slowdowns.

About the only time I had a big slowdown with radioshift was trying an experiment in which I was recording about 20 streams at the same time.... LOL

Brent: one other question: were you using the 10.5.6 update of 10.5? with a Firewire drive? on the support.apple.com area there are a lot of people (including me) having huge problems with 10.5.6 and firewire devices.