Anecdotal, but VirtualBox has always been a bit flaky for me.
VMWare Fusion, on the other hand, powers the desktop environment I've used as a daily work machine for the last 6 months, and I've had absolutely zero problems other than trackpad scrolling getting emulated as mouse wheel events (making pixel-perfect scroll impossible).
Despite that one annoyance, it's definitely worth paying for if you're using it for any serious or professional purpose.
VMWare Fusion, on the other hand, powers the desktop environment I've used as a daily work machine for the last 6 months, and I've had absolutely zero problems other than trackpad scrolling getting emulated as mouse wheel events (making pixel-perfect scroll impossible).
Despite that one annoyance, it's definitely worth paying for if you're using it for any serious or professional purpose.