you'll generally find that most of the ETFs and similar products (i.e. spdr's) are not very liquid at all, and thus kinda suck for active trading. in fact, so few people trade them that i wonder why they even have them. maybe it's to make the AMEX feel like it actually counts as an exchange. and because most of them are traded on amex, the spreads will kill you. this is because there's no consolidated quote - mixing no liquidity with no island visibility to non-daytraders is not a good combination. even if you wanted to try and scalp these stocks, most people who trade them wouldn't even see your bid or offer, since they aren't daytraders and are looking at whatever quote schwab, fidelity, or etrade is giving them.
you might check out load funds. they might end up being cheaper in commissions (and don't have spreads to eat your capital).