I still use it for two main reasons: Nostalgia and Challenge.
Nostalgia, because the Amiga is the first computer I ever really got into, mainly for music composition and desktop publishing.
Challenge, because it is a lot of fun trying to get the system to do modern things it was never designed to do in the first place.
My main Amiga now is an Amithlon. With it I have connected it to the Internet and my home network. I also have set up a CD-burner on it as well as USB capability.
Using RDesktop, I can remote into my WinXP machine which I use as a pseudo-Bridgeboard to run FireFox and other modern apps which we don't have on the Amiga. I've also used TwinVNC to remote into an Ubuntu Linux box.
It's neat to have Amiga OS3.9 running on a 1280x1024 32-bit color screen, and it's blazingly fast. I also have ShapeShifter to run my old Mac programs (System 7.5).
It's also neat to play CD's and MP3's as well as my old Mod files.
For Deluxe Music, I still use my old classics. Nothing can emulate the warmth and accuracy of the original Paula chips.