I´ve been a long time user of both Paralells and VM Ware Fusion and none of them have been slower then using an Atom based PC. Would be interesting to know how you configured the virtual machine to get suck poor performance...
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I just installed it on my 2.3 GHz MacBook according to the directions, with pretty much all the default options. Nothing out of the ordinary. Gave it plenty of disk space. At first it did run at an acceptable speed, but became bogged down soon thereafter. I tried reinstalling twice for each version, as I recall. I used both versions 7 and 8 with Windows XP. After the reinstall it was OK for a while but then bogged down again. I pretty much just used it for Word and Excel. By the time I gave up I could go get a cup of coffee waiting for a file to load.
The little ATOM is actually fine for Word and Excel, which are not particularly demanding applications. I gave it a bunch of RAM and it handles the Office apps very well. I wouldn't run Adobe CS6 Design Premium on it! Or try any major league games! But with Word it zips.
Parallels strikes me as a very elegant solution, but for me it just wasn't practical. Bummer.