Which pages of the thread did you read?  If only the first page, it's rather out of date.
Qemu has always been free.  VirtualBox is free, however the "full product" isn't open source (should be of little interest to you).  VMWare have a free Player and Server.
So in a sense, they're all free.

Qemu+kqemu is definitely much slower than VirtualBox and VMWare for me.  I don't know about KVM.
I wouldn't really consider it "difficult", rather, you just don't really have a nice GUI to configure things with (they do exist though).

But of course, for playing around, that's fine.  Also if you want to run a different platform, qemu is useful, though probably mostly for emulating Linux/BSD etc.  I think qemu is also probably the best pure user mode x86 emulator, if that's important to you (eg running it on a school/work machine).  Windows XP ran rather slow for me in qemu+kqemu however.

(This post was last modified: 21/02/2010 11:01 PM by ZiNgA BuRgA.)