I have also got that beta.
I had a little problem with the installation, I tried to do a clean install directly from the CD but somehow the installation program said there were some files missing in the CD, I ignored it and once I installed it I got lots of problems, I couldn't open system propieties or the Internet Explorer.
I formatted the partition, installed Win98 SE, copied Whistler to the HD and updated it, it worked all right.
It is quite slow compared with Win2k, but note I am running a P200 MMX with 64 mb of RAM.
IE 6.0 usually hangs when you get into web sites which use flash.
Don't you think that M$ shouldn't charge people for trying their software and helping to improve it?