Thanks to QuickGPS application (see below: this application in action in a video!), that is included in the HTC Touch Diamond, the GPS fix can be accelerated by downloading satellite data from the Internet from time to time:

... and thanks to high-resolution display (VGA = 640x480 pixels) viewing maps is pure pleasure (here: Microsoft UK headquarters):

Screenshot above is from TomTom 6 that works perfectly in HTC Touch Diamond but TomTom 7 is already available.
Note that while TomTom is the best GPS software (that uses maps stored on memory card or internal storage - no online connection needed!) for turn-by-turn navigation, sometimes it is showing less points of interest (here: cinemas in vicinity of Leicester Square in London, UK):

... than Google Maps (the improved Google Maps especially designed for HTC Touch Diamond, with fancy red pins dropping from the top, is pre-installed in this phone):

... so we advise you to youse Google Maps, and other similar programs from Yahoo, AOL and Microsoft (Live) - to get most up to date lists of points of interest. For turn-by-turn navigation however applications like TomTom are the best because they show you the way to go - both visually on the map and through voice instructions.
The QuickGPS application automatically can notify you after a couple days when your GPS satellite data download from Internet - used to accelerate GPS fix - has expired. Here is a video demonstration of expiration of this satellite data and how this program is working (downloading current GPS satellite data from the Internet):
Conclusion: GPS in HTC Touch Diamond is really good.
msmobiles.com