I'm going to a gym where the bench has a ton of SOFT padding. About 3". I don't know how much of a problem this is a for benching, but for DB rows it's almost unusable. The padding goes down more than an inch when I do rows (didn't check for it when benching).
Long story short: is benching on this dangerous for my shoulders?
A soft bench allows you to dig your traps in and get better leg drive. My current gym, a commercial one, the benches are firm and I slide. I have to get a carpet runner. Some dude suggested it once here on T-Nation and sounds like a fantastic idea.
Not quite dude..all the competition benches and better quality benches have dense padding and Naugahyde covers. You want support but not a Tempur bed to bench on..lol
Maybe so on digging in your traps but like I said above REAL benches are dense foam. The reason you slid off the bench is because all of the peoples "MANG" ie.body oils and sweat have soaked into the vinyl covers and they have become slick. I wash my bench off with 409 or another degreaser from time to time to prevent this. Carpet runners are a great idea as well as YOGA mats from the bunny corral if you don't want to spend $6 on a runner.
I personally like my bench firm almost hard. On a softer bench when I get the hand off, on a softer bench I sink in uneven to the point where you lose stability. And on the slipping thing, either the material is shitty or the like StrengthDawg mentioned, the nasty "mang". On one of the "comp" benches at our gym, the bench cover is pretty shitty and we just take two average bands and wrap it around the bench, no more slipping.