Just installed the PB4 on my daily driver machine and am actually quite happy. It doesn't have the hang ups like Mavericks did, and I find the design aspect great too. Went back to Mountain Lion after Mavericks seemed to slow down my comp. No spinning ball as much anymore. Some apps freeze a bit, and close, but thats to be expected. Was thinking about getting a new iMac this year, but with this update, I can probably hold off for another year, or until I fill up the HD again! LOL, 320GB isn't near enough. For reference, these are my specs.