I'm not much of a WA lens user as I don't shoot much landscapes. The only "WA" lens I have is the Nikon AFS 17-35mm/f2.8... and that is not wide on my D300 due to the crop factor (equivalent to 25.5mm to 52.5mm on 35mm format).
But, thanks to Tamron, the new Tamron SP AF 10-24mm/f3.5-4.5 lens was made available for me to test. This lens was announced in PMA 08, and you can read all you want about the nitty-gritty here in DPreview.
Tamron has an earlier WA lens - the Tamron SP AF 11-18mm/f4.5-5.6 Di II LD. From the way I read it in their promotional brochures, it seems this 10-24mm is a replacement for it. Not a bad option, IMO, cos I always thought the 11-18mm was a little slow at f4.5-5.6 anyway. For those who want to know how the earlier WA lenses stack up against each other (at least for the nikon-users), please refer to this.
Here are some impressions of mine about the lens. This is not a scientific review. And I don't want to pretend to be as exhaustive as Phil Askey. If you want something more scientific, you'll have to wait for DPreview.
#1 - How the lens look on my D300.
The lens itself is pretty lightweight and compact. I've used/owned 2 Tamron lenses before (the 90mm macro and the 28-75mm/f2.8). If you are familiar with Tamron lens construction, the built of the 10-24mm is roughly similar - mainly plastic body with a metal lens mount. It is, as some online reviewers said of other Tamron lens, functional.
#2 - Exterior of lens
As mentioned, it has a metal lens mount. The only other button it has on the body is the M/AF button.
A simple distance scale is also available. As you can see, it can close-focus to 0.24m (not macro).
Fully extended. As you can see, it still maintains its compact size. Its 77mm front element is non-rotating, a boon for those using polarizing filters or GNDs.
#3 - 10-24mm vs 17-35mm in size
This is how the 2 lenses compare in sizes.