I started using provisioning to deploy Vista machine (800 PCs) two years ago with no problems.
It's true that credentials are in plain text in unattended.xml but it's the only issue I have
I can use wildcard and pull the computername using bare metal and install scripts.
As Jary and others have indicated, it is doable and many people have this working. I guess what you are looking for is a more integrated process Provisioning of Vista/Win7. Something where you don't have to download Jan's HII (it is a great bunch of scripts/docs but should be integrated into the product), read this doc, hack this files, etc...
The only way you are going to achieve this is speak to LANDesk concerning what you want in the form of ERs. Personally I think there are two main paths for LANDesk concerning OSD. One - Compete directly with Microsoft's MDT feature for feature and produce a better product (this should not be too difficult), or offer functions/procedures that make MDT better - enhance MDT (sort of what the HII product has done for LANDesk). IMO I think you take the best parts out of MDT, fill in the holes of MDT, and enhance the current LANDesk provisioning stuff to create a supper LANDesk OSD.
There is a newish Vista Sysprep doc here http://community.landesk.com/support/docs/DOC-5779 and it does discuss deleting of the unattend.xml. You can also make this apart of the provisioning task or a custom vuln.
So it is a good time to hit LANdesk up with your ideas and suggestions about OSD.