Don't know much about Borovets for skiing, although as mentioned by someone earlier, the fact that it is (perceived to be) cheap means you get alot of neg-ends going there for a bargain holiday.
Oh and by the way, watch out for the Gypsies and the mafia!
Before anyone gets all high and mighty about being racist etc. I've seen it with my own eyes!! Gypsies (proper Romany ones) are treated as the lowest of the low, consequently they have no choice but to revert to pick-pocketing, begging and theft to survive.
As for the mafia, I've never seen as many big, blacked out, BMW's as I did in Bulgaria. A friend of my missus was car-jacked and then asked/told to 'insure' it with a local crim if she wanted to get it back. Nice place!