Yeah, pits can be very fun. But they aren't used properly in most levels. So letting people know where pits are is a great idea. Having some kind of lava, water or signs is what I think is a absolute must. Also you should not just add pits randomly, it needs to have some kind of purpose, like making a power up harder to reach. You can also have a shortcut to the enemy flag where there are dead pits, so if you take the risk by taking the shortcut you will be rewarded by capturing or scoring the enemy flag much faster. So id say, go ahead use pits, but do it with purpose and think well before placing them in your level.

I think I used pits pretty good in Extraterrestrials where they are in obvious places and the river of acid let's players know that there isn't anything else down there but certain death.