You think the 1.42 GHz mini multitasks better than the Athlon 3500? Wow, I have an old 1.4 GHz Athlon with 512 MB, a 9600 SE w/128 MB and it multitasks rather well for being 3.5 years old. I run Firefox, Thunderbird, Trillian, iTunes constantly with services running in the background (webserver, MySQL and Prime95 not to mention the usual - Norton, etc.) I'm also a programmer and have no problem running a VMWare session and compiling in VS.NET 2003 at the same time. Could your Windows machine be bogged down with malware?
I have a Mac mini 1.42 GHz (full specs in sig) on the way. I just ordered last week and it is supposed to ship on March 3rd. I am expecting my Mac mini to be on par with my PC perhaps a little snappier with Apple's software since it's optimized for their hardware. I played with a mini at the local Apple store and performance was decent, but it only had the stock 256 MB. I'm getting 512 MB in my mini because I didn't want to pay Apple for the gig stick. How much memory did you get in your mini? I'll probably be asking around the boards if 1 GB really helps the mini fly I might upgrade it myself. Most reviewers said 512 MB was the sweet spot, we'll see.
Still, if the mini performs as well as you say I will be very impressed. Now I just have to wait...