You also get a smaller piece of the pie compared to guys who generate much higher Hashs. If you luck out on the smaller pools you gain more as the pay out will be higher. Arsbitcoin has been pretty decent since their payout system (PPS) is different.
I think that's another myth. If you're mining at 100 MH/s and someone else in your pool is mining at 300 MH/s, it doesn't matter if the block is found in 1 minute or 10 minutes, he's getting 75% and you're getting 25% no matter what. There's no bonus as far as I know to being the person who actually found the block.
Depends on the pool.