I work with vm's all day long and last I tried virtualbox (about a year ago) the commercial products were worth the money paid. Back then virtualbox would randomly crash after 15 minutes into a 30 minute compile job on Linux VM
With Parallels upgrades being $40 or less (and Fusion similarly priced), it is worth the price of admission to get the polished product.
I've been using virtualbox for years?
I don't know, have you