I'm playing in a campaign right now, granted its 2nd Edition. It's been a long game session, currently My Mechwarrior is -1/-2 with NA Pilot and Gun Mech. The game master has no problem with this, I asked if I could have skills go into the Negatives and He was fine with it. We get together 1-2 times a month, and sometimes he hands out AP like candy. When I run games, I like it when the players have a high pilot and gunnery skill. However, if you tend to run a long campaign, Your players will more than likely have some pretty good skills with good levels. All you have to do is up the difficulty of the sessions, or just start a new campaign.
I used to have a GM, that would run snuff campaigns once a year. You knew going in that your character was going to die, but that was the fun of it. It was a great way to end a long campaign, everyone always enjoyed it. If you didn't want your character to die, you didn't show up for that session.