Halloween 2011 is on a Monday. I don't think that is a bad day for it. I've always preferred weekday halloweens as opposed to weekend halloweens.
Why?
Well, I prefer weekend parties. I generally prefer to throw my halloween parties on saturday. That gives me plenty of time to finish prep the morning of. If I have a party on a weekday I have to do the last minute stuff the night before or take a day off work.
I also think saturday parties work better for most people. They're more refreshed from not having a day of work and they have plenty of time to get ready... a must for a halloween party.
But wait, you say...you said you prefer weekday Halloweens but are talking about saturday parties.
Good catch. I n addition to not having weekday parties, I don't like to have my parties on Halloween. I prefer to have them a couple days before. If a party is on saturday, and halloween is on saturday, you'll get less of a turn out. More people will have commitments like kids. Better to have a kids halloween night during the week, and adult halloween on saturdays.