I use market orders all the way. I am not going to haggle over pennies, becuse if i do, i run the risk of not getting into the position.
If i want in..it is becuse I have done my homework and dermined the trade to be viable and potentially very pofitable. So i just get in.
I Dont daytrade, and find one of the disadvantages to daytrading is the need to rely on execution to be profitable.
Another thing is liquidity. If you are trading something that is liquid enough..the spread shouldnt kill you...in stocks at least. options are another story.