For me, OSX + VMWare is my ideal testing environment. As virtualization comes into play more on desktops, that could marginalize the utility of a browser-based

For me, OSX + VMWare is my ideal testing environment. As virtualization comes into play more on desktops, that could marginalize the utility of a browser-based solution for this, although presently I think it's an idea that is definitely useful and price-wise they offer good value. I haven't used virtualization on Windows or Linux much, how are those at testing other platforms? All the major browsers already run on Windows, but I've been bitten by differences in Firefox between Windows and OSX before (line heights were off), so multi-OS testing is still important.