You could probably get around the slowness somewhat by pre-advertising the auction schedule, and people could make sure that they or someone they trust is around to bid for them when the auction price hits their limit.
Could you not alleviate that by allowing people to put in bids below the current dutch auction price? i.e. say the price is 50BTC, someone can post that they want 4 @ 45. So they don't have to constantly monitor things, they can just take the risk that if the price falls to 45, they will get 4 for them to pickup (provided they are the first bids).