My grandfather has it and he's taking a strong liking to it (he didn't have any time for his previous phone).
I've used it quite a lot too and had every intention to get one myself until Google released the Nexus One which I am now planning on getting instead.
The only issues I've had with his are a slight niggle when linking up to his car's Bluetooth system (Jaguar), and also the Wi-Fi wasn't very reliable at first, but seems to have resolved itself somewhat.
There's plenty of reviews on the internet of the phone if you look on Google. Just search for HTC Hero, rather than G2 as only T-Mobile name it that. The rest of the World calls it the Hero.