In reply to a13x:
Getting a 29er 4 years ago dramatically changed my MTBing, from something I did occasionally to my main hobby (displacing climbing, for now at least)
Unless you're a midget or are looking for a downhill only bike then 29ers are a no-brainer IMHO. You go faster and roll over minor obstacles with ease. And if you're tall, then you are less likely to go over the handlebars, so I've found I have far more confidence going downhill.
The only drawback is the obvious one - longer wheelbase, so really tight corners are harder. For red runs at trail centres it shouldn't be much of an issue.
I've got a Trek X-Cal and been very happy with it