I'm not a BitDefender user, but I thought I'd add some comments until such time, a BitDenfender user comes along.
You didn't specify which version you're interested in. The free version? BitDefender Antivirus 2010? BitDefender Internet Security 2010? It would certainly help to know.
If it's the "BitDefender Free Edition", consider reading through the two pages of comments of user reviews at CNET Download.com.
The next place I would look is at http://www.av-comparatives.org/. Here you'll find the results of independent tests of different A/V software. It's one of the more reliable sites.
I'm not a big fan of reviews, as I would rather hear about software from user's. Especially a user I know. Since that's not always possible, reviews have to be considered at times.
I randomly picked the following reviews, only because they didn't paint a perfect picture. It may not be a justifiable reason, but I'd rather read a review which indicates a "drawback or two". Perhaps, they're being honest. Perhaps, not.
Note the two different versions:
Review of BitDefender Antivirus 2010
BitDefender Total Security 2010
Reviewing BitDefender Internet Security 2010
I hope you find the information you're looking for. I sometimes find going to the dedicated forum helpful. If I see the same (and constant) complaints, I might second-think installing it. You may do things differently.
Best of luck..
Any BitDefender user's out there, How do you like it??