I would never jump in on day one. I view OS upgrades the same way I see the opening up of a new restaurant:
Let everyone else be the guinea pig. A restaurant opens... There is a new cook, new waitstaff, new supervisors. They've been trained well but grand opening day will be an interesting experience. The staff will be operating in the real world and under live fire as they open their doors. Sometimes mishaps occur and the experience is less then pleasant in the first couple of weeks.
I'm excited to try the new restaurant but I'm willing to wait a couple of months before I visit. I want them to iron out the kinks before I visit.
You should create a checklist of all your mission-critical applications to see if they work well in Mountain Lion. I remember Microsoft Office 2011 was not quite ready for Lion when Lion was released - in particular their Outlook program. It took a few months before Microsoft finally issued an update.
Take your time with Mountain Lion unless you don't mind not experiencing possibles headaches with some of your mission critical applications.