One of the big limitations you may have noticed with apps like ShopSavvy or even Microsoft's own Tag app is that live-scanning of barcodes is not permitted--you have to snap a photo, which is then scanned before a look-up is performed. It is technically possible but Microsoft is not allowing developers access to the APIs necessary to implement--not yet at least. [Edit: Although LG does have a live scanner called 'ScanSearch' available on the Quantum and Optimus 7]
Sensboston, who's been doing lots of neat tricks for our new OS (e.g. flashlight), has managed to use the previously documented API to release a working scanner. Based on zxing library and Kevin Marshall's (from Clarity Consulting) code, the app works like other barcode scanners on other platforms: you turn it on, it live scans and gives results. The app works offline, can save info to email or SMS and searches for info using Bing or Google.
You'll need good light for it to work and the auto-focus seems to time out after about 15 seconds (save battery?) but overall, it works pretty darn well. Sensboston is looking to add features/improve the UI, so if you have any ideas, let him know in that thread. Looks like the hombrew scene is raging these days...
Source: XDA Forums; Update: Project is now open-source