HTC mains-to-USB charger: use to charge other non-HTC but USB-chargeable devices? My HTC Desire Z came with a charger that consists of a mains electric plug with a USB socket for attaching the phone to to charge via USB. 

Other devices such as the iPod touch can be charged via USB.

Assuming that there is a standard for USB powered charging, i.e. a amp/watts/voltage rating, then could these devices be charged from the same adapter, safely and effectively. 

This would save money buying additional mains adapters, when, for example, the iPod touch does not come with a USB mains charger, though it does come with a USB sync cable for iTunes and also for USB powered charging from a PC.
I treat chargers with the same specs as interchangeable... many USB chargers are rated as 5v 500mA (or .5A); in most cases, you should be able to interchange them (it may take excellent eyesight to actually read the specs; on my Motoroloa chargers, they are very faintly engraved).   Some Apple chargers produce more current than the standard 500mA, so I would not use them to charge products other than the intended.   Since most computer USB ports are rated for 500mA, chargers with the same rating should charge any USB-chargeable device without problems.