OK, I've got Scottrade and their rules say that you can buy and sell any security 3 time over any 5 running day period. If your account is under 25K and you have a margin account the day trader provision classification goes into effect if you buy and sell on the same day a 4th time over any 5 running days. If your account is over 25K it doesn't apply.
Now, if you buy on Monday, sell on Tuesday and repurchase the same security on the same day, this isn't considered a round trip. At one time it was and they changed the rules so that it's not.
In my case having a margin account is very convienient because it allows me to go right into another security right after selling out of a position. If something happens that I either like or don't like, I'm able to liquidate without repercussion. Like Chart says " use this primarily for defensive purposes". Now, if I get a huge quick run up I will on ocasion take that with my limits in mind. Hey if I run out of round trips I get to go do something else! Long weekend! LOL
PS: As a side note: When the market is down I tend to establish positions in the latter half of the day so I can sell the next day if needed.