I work in a T-Shop + own a Desire. Very frustrating dealing with customers wanting the update already!
Given the fact I work in a shop...am privy to all the information regarding updates....I've STILL rooted my Desire and never looked back.
Some people have thought it'd affect Next G coverage - nope. Balls. All still good.
To be honest, you'll be waiting another month at LEAST before Telstra will release it, especially over the air.
There was a second update on the HTC Website, but it doesn't actually say what the update is...might be worth a look maybe.
ROM Upgrade for HTC Desire (Telstra)
Dave
HTC Desire
Rooted
LeeDrOiD_V2.1a
DeFroST 4.9
Virtuous