Do it!
Riding Rotorua is awesome. As the others have said, locals are friendly and you can buy a trail map from the bike shops in town. I was over there for a holiday with my wife and had one day in Taupo and one day in Rotorua at the end of December and it was the best days riding I've had!
Did the W2K track at Taupo and most of the trails in Craters of the Moon all in one day. They were all great, and there's plenty of other stuff to do in Taupo like jet boating, kayaking on the lake etc.
Then there is Rotorua! Many more trails and more variety. I only had one day there, and would've liked a few more. I had a trail map and was finding my own way, then hooked up with a local at one point. We were of the same ability and he was really cool and let me tag along while he showed me his pick of the trails. Tried to cram in as much as possible in that one day and had a ball and was exhausted by the end of the day!
I had no mechanicals at all, but the local bike shops looked very well equipped to look after you, but I made sure I took things specific to my bike, like a derailleur hanger. I took my hardtail 29r with me from here, and it was perfect for almost all of the riding there as most of it is quite smooth singletrack. A 5" travel or so trail bike would also be great. We flew Virgin Blue to get there and Air New Zealand back and didn't pay any excess baggage, but we only checked in 2 bags, my bike in a box and a suitcase. Don't forget you can't take CO2 cartridges with you on the plane. As we were there for 10 days total and traveling around, we had a hire car. But if you are staying just in Rotorua you might be able to get away without one, as you can ride to the trails easily from town. If you want to get down to Taupo it might be a bit harder though. My wife doesn't ride, but while I was off MTBing she enjoyed a day spa and then a walk in the Redwood forest, so we were all happy! Oh, make sure you have a go of the tobogans too!
Can't think of much else right now, but the AMB article was pretty spot on.
Have fun!