Women are like:

...the stock market
They're irrational and can bankrupt you if you're not careful.

...computers
They take too long to warm up and a better model always comes along once you've already got one.

...Saran Wrap
Useful but clingy.

...horses
Fun to pet and ride but a pain to feed and clean up after.

...parking meters
If you don't feed them with enough money you face serious consequences.

...fax machines
Useful for one very specific purpose but otherwise just high-maintenance paperweights.

...political campaign contributors
If you let them talk about themselves long enough you wind up in bed with them.

...refrigerators
They're always cold and never seem to have a beer when you need one.

...blue jeans
They look good for a while but eventually they fade and have to be replaced.

...country western songs
They're annoying, they all sound alike, but if you really listen to them you'll get depressed and drink a lot.