While, as others have stated, rubber w/ studs has it's advantages on the shore, I tend to be of the opposite opinion to PennKev for my personal use. I spend far more of my fishing time and walking *in* the water, and on land I'm far more sure-footed anyway. I need the best traction available while I'm actually in the water, and for me, that means felt, every time.
I don't believe we'll see felt outlawed in PA ever...certainly not within the next decade or two, especially with many scientist now determining that felt soles (or the banning thereof) doesn't significantly impact the spread of invasives one way or another after all.
If through some turn of events, PA would outlaw felt, I'd still be using it for most of my 'out of the way' fishing. The PFBC isn't about to pay my medical bills if I slip and fall in the stream, so I'm not about to have them dictate to me that I can't wear what gives me the best traction.