I wasn't sure if SLUSH used a 1% transaction fee or not - after seeing the warning about using an outdated miner, I suspect that it is actually 1% - the warning stated that if I didn't upgrade to a stratum-enabled miner, or set up a stratum mining proxy, the transaction fee would be raised to 10%, from 1%.
Slush doesn't have a transaction fee. The fee (2%) is the pool fee which comes straight out of the rewards.
"25 BTC + block fees - 2% fee) * (shares found by user's workers) / (total shares in current round)"
The increase to 10% is if you're still using old getwork and haven't moved up to stratum, to encourage everyone to change to the more stable and maintained stratum. If you are using guiminer (most newbies are) then it will auto convert to stratum, from http://api.bitcoin.cz:8332 > stratum.bitcoin.cz:3333, however still better to using stratum.bit:3333 etc. in order to not have to "go through" the old getwork. If you are not using guiminer and still using the old api.bitcoin.cz:8332 then you either need to using slush's stratum proxy (found on main site) or change to stratum.bitcoin.ca:3333.
This is explained in better detail (and more accurate than my poor retelling) on the slush thread.
