Frictionless Long pips
As a coach, I've spent a lot of time over the years thinking about long pips, both how to play against and with them, and about whether they should be legal. My thinking on this has evolved over the years. I admit I'm somewhat skeptical of the pure long-pips blocking style, especially when a player basically covers the entire table by just reaching out and blocking everything back dead with long pips without sponge. In my opinion, it simply isn't very athletic, and table tennis is a sport. But it's legal, and as players and coaches, it's our job to figure out how to play against any legal surface. Besides, if you were to ban long pips, you'd essentially lose the chopping style, which is truly athletic and great for spectators. Plus not all long-pips blockers just stand there and block - some play an athletic forehand game, with the long pips often more a weakness than a strength.
Recently there's been a lot of debate about frictionless long pips. The ITTF made a regulation a while back that they are illegal. (Technically, no surface is frictionless, but they are defining frictionless to be under a certain amount of friction.) Some have taken legal long pips and baked them in the sun or treated them in some other way to make them frictionless, and argue that that's okay. It's not.
If a referee judges that the long pips are frictionless, then he knows that they have been treated in some way to make them frictionless. USATT rule 2.4.7 states, "The racket covering shall be used without any physical, chemical or other treatment." So when a player does something (such as letting them bake in the heat) to make his long pips (or antispin) frictionless, or does something similar to an inverted or any other covering, he is cheating.