You may be surprised how often someone purchases a Mac OS X upgrade, reads about the installation process, and then leaves the DVD in a drawer for months. Some people habitually wait until the first or second minor update after a major Mac OS X release before taking the plunge, whether to give Apple time to work out all the bugs, to give developers time to update their applications for compatibility, or to see how other people like it before committing themselves. And others feel nervous about upgrading until it's nearly time for the next major version to be released! Don't let this happen to you.
I'm an early adopter, and although I've experienced my share of minor hurdles, I've never regretted a decision to upgrade immediately. You may, however, wish to delay an upgrade if you're in the middle of a project and can't afford any downtime, if you rely heavily on an application that has not yet been updated to work under the new system, or if you expect to buy a new Mac in the near future (which will, of course, include the latest version of Mac OS X).