i have found that a catalyst can severely hamper the effectiveness of certain stocks, for usually a week or two. you get filled on the same side almost every day, and you get hurt. it is often triggered by a significant news event.
a few examples: SBC, getting filled several times in the past two weeks - all shorts and all losers, until a short ended the route a a day or two ago. this after there was significant news in verizon.
i noticed the same on NKE a while back after it reported earnings. kept getting short, kept getting hurt.
JPM was bad the past two weeks, and there has been significant news there.
TXN has been horrible the last three or four fills or so (i don't have the spreadsheet in front of me), but it was great before that. this is somewhat of an exception, as i'm not aware of any recent news
WYE ...was really bad a while back, you kept getting filled on the long side. this, after some negative developements. it's been good lately. i don't trade it though.
there are more....
i just completed my first month with this, so with the exception of the actual news day, i wanted to follow the rules. but now, if there is a significant event, i'm going to take the stock off until there is a profitable trade or two in it.