There are a few reasons your pictures might look flat when you preview them in Adobe Bridge. It's essentially reading the metadata and applying it to the preview image. Check your cache settings, and try purging the Cache too.
Also make sure it's not using software rendering, let your hardware do that for you. In Edit / Preferences / Advanced, uncheck Software rendering. And then also make sure your color settings in Photoshop are correct. More importantly, Make sure your monitor is properly calibrated.


As far as Vignetting a picture you have a couple ways you can apply or correct a vignette. In ACR under the FX icon you can do as already described and set the post crop vignette. You can also use the Lens Correction to apply or correct a vignette too. And then in Photoshop under Filters you also have Lens Correction where you can apply or correct a Vignette. if you're creative you can make the vignette any color of your choice.


To familiarize yourself more with CS5 I recommend reviewing the Videos at Adobe TV in the following first couple links. I'll also include a few other links to great video tutorials for CS5


Learn Photoshop CS5


Photoshop CS5 Feature Tour


Max 2010 Photoshop Session


Planet Photoshop


The Russell Brown Show Tips and Tricks


Using Adobe Bridge