hardly. at least i haven't found one yet. however, if you play very well with your style of play(long balls, or direct passes, or short passes) you are likely to get a reward for that. he who plays well gets the result imho (in multiplayer games)
Hmm... sorry but that's too nice a picture.
1) Most people online in PES play with either Brazil or Inter, the two top teams in the game. Yes, they are hard to beat, but not impossible.
2) In PES 2008 you have two "bugs" mainly: scoring from midfield via a long pass when the keeper is far from the goal, and scoring via a corner kick by sending it directly to the keeper, who fumbles it in in a great deal of occassions. They are not that easy to make, but you know how it is, some people will surely practice them and do them over and over during a game.
3) There is an infamously easy way of scoring also, known as the cutback. These consist on you running down the side of the opponent's box with someone like Ronaldinho, C. Ronaldo or whoever, and then cutting it back to the middle for a free forward to bury it. These are very easy to make, particularly if the player running down the wing is skillful and can run rings around the defenders until an attacker is left unmarked in the box. There are a lot of people online who do this over and over. It's hard to defend and easy to make, which is a bad combination.
So there you have it, PES online is fun, but it's not paradise. My advice is to get in contact with people who like to play the game with different teams, don't exploit the bugs and try to restrain from cutbacks unless a chance for one of them presents itself naturally.