I really don't think nice guys finish last. Sure, being the Nice Guy comes with pain and challenges, but overall, you are better off. At least at the end of the day, you know you did the right thing and will always have that to fall back on. But there's a difference between being nice and being a pushover. Sacrificing your leisure time every once in a while to help out a friend is good. Sacrificing your leisure time because your "friend" has alienated all other friends and is using guilt trips and pouting to ensnare you is not good.
Dear Drama Mamas,
I am an officer in a casual raiding guild. We were running 10-man ICC with a core group of about 12 people until the summer slump hit. As we progressed, we started getting all 12 people showing up on raid day, so we had to choose. The problem came when one of our DPS was showing up on time but was constantly going AFK, not paying attention, and being obnoxious in Vent -- generally holding the raid back. He started getting skipped over every time extra players were online. When he outright asked about this, the officers decided he was always going to be last pick. I insisted that we tell him that he was on backup status and why. The other officers didn't think it was necessary to say anything to him, but I did it anyway because I felt it was the right thing to do.