Bought Warhammer 40,000: Dawn of War II when it was $30. I've only played a little so far, but it's awesome. I don't like standard RTS games, but Dawn of War II is really fun. (I have StarCraft II, but haven't played it more than a few hours.)
Borderlands: Boring. I got GOTY for $15 or $20 a while back, but I wouldn't say it's even worth $7.49. It's an unusual game in a few respects, but overall very standard, monotonous. Drive around, shoot stuff. The art style looks interesting, but gets very dull after a bit.
I'm going to contribute and say I ran into a similar Borderlands situation. Everything in the game was relatively easy, until I faced the bandit leader next to the town. He and his 2 companions would not die. It took each of the underlings more than 7 head shots with a ridiculously powerful sniper rifle to kill. It took me 5 tries and the leader standing completely still for over a minute to down him - well over 20 minutes spent just firing shots into his head. This is all head shots, very high-power sniper rifle, sending my hawk as much as possible, not taking fire from anyone else. About an hour of my life, wasted in frustration. It wasn't even a hard-ranked mission. At one point, because I felt like it, I went on a very hard mission; it was a nice challenge. That boss fight was just ridiculous.
Anyway, Steam sales are pretty great. I've gotten some great games I wouldn't have otherwise. (STALKER, for example.) I frown upon them for tempting me to spend money on poor games, though.