Hey Jason, I am definately very happy with my Squeezbox. I had my doubts as to the interface, and how easily/quickly I could navigate my large music collection, but the Squeezebox is great and I have no complaints.
My story is similar to yours. I never used a SLIMP3, though mainly because I never had the extra cash, being in school at the time. I'm a huge supporter of open source, and have recently switched to Macs due to their blend of open source and quality design. SlimServer and Squeezebox integrate really well with iTunes, expanding the availability of your music collection while keeping it easy to organize at the same time.
Hope you enjoy it as much as I have mine.