I've installed the program on 3 computers, it slows them down even when not scanning. Sometimes the computers even don't respond for a certain period (without having other tasks).
On my main developer computer I haven't installed any other AV/Firewall programs, the main problem here is that Bitdefender gets choked in the file versioning program that I use (SVN). It contains a lot of nested invisible files and Bitdefender treats them as rootkits. Eventually Bitdefender needs all system resources and isn't able to complete a full scan, in the end it gets stuck and its serverices are disabled.
To be short on this, I'm not happy with the product and I asked my money back (which I'm still waiting for after 10 working days).