Many of you have asked me if you should upgrade to Mountain Lion. I have been using it for almost a week now, and like it. But, compatibility with older apps is an issue with all upgrades, so here is s a link to a table of apps and their compatibility:
This table is like Wikipedia, it depends on reader contributions, so it's not 100% reliable, but I have found roaringapps.com to be a pretty good source.
If you don't see any reported problems with things you count on, I would say it's a go. Note the somewhat murky reports of Photoshop CS4.