Always shower with a chivalrous friend who can hold the curtain away from your body.

If you leave your shower curtain long enough without washing, it'll be too stiff to try and cling to you.

Alternatively, hang weights on the bottom of the curtain?

To paraphrase a great thinker: I can't fix it, but I can explain why it happens.

Straight Dope.

Velcro. The self-adhesive type, heavy duty. One side along the edge of the tub, the other on the bottom of the curtain. Or at strategic points, whichever is best. Make sure both curtain and tub are completely dry before attaching the velcro.

I have used rocks to hold the bottom of my shower curtain down. I thought of using velcro, but rocks were funnier. That happens when I only have the plastic liner up, when I have the cloth outer curtain hung too it doesn't happen, but if the cloth curtain is in the wash, the plastic curtain flies like superman's cape.

Nah, don't do any of that. Just put soft, silky smooth strips on the inside of the curtain and enjoy as it puffs and slides into you while showering...

Don't have the knobs turned up so high. Seriously. My place, I've got one of those regulated shower heads, and you don't, and how many times has my shower curtain latched onto your bod? None. The more water that is moving through the shower increases the amount of suck, and causes the curtain to get all uppity.
Fact.

Yeah, but I LOVE having a shower that can double as riot control. If a riot ever broke out in my shower. You never know. I guess that's the compromise I'll have to make. Damn. I like essexjan's and getoffmylawn's suggestions, though. Or, riffing on croctommy's suggestion, I could always get a Benicio del Toro or Gary Oldman shower curtain. Or have your image lasered onto it.

If your bathtub is metal, tape neodymium magnets to the bottom of your curtain.

A lower-tech approach is to get the curtain wet between the bathtub and the curtain. Surface tension will hold the shower curtain to the bathtub.

I really liked croctommy's response. Just like those crazy strips at the drive-thru car wash.

You go naked in the car wash?

Liners, I find, are the worst offenders. The heavier stand-alone shower curtains don't seem to billow so much (maybe use one of those, even as a liner, if you like the cloth curtain/liner combo).

Zack has it. Try different shower heads that reduce the power(speed) of the water. (If you can stand this!)This is one example of the Bernoulli effect when the water coming down the shower head with large speed creates low pressure center (streamline) that sucks the curtain inward.

Also, I never, ever use liners (and I hate hotel showers for this exact reason, but then I always put the curtain outside the tub, which helps but messes up the bathroom, but who cares I am not cleaning it!). I use clear plastic (sort of more heavy set) showers curtains (this one!) which are harder to pull. It works!

Shower Curtain Man would make an awesome superhero.

It was Scientific American's (former) Amateur Scientist that managed to first answer the question of why the curtain does what it does. I don't think Cecil or his letter-writer gives them credit. The SciAm article used smoke generators to track the airflow. It's the Bernouli Principle and doesn't rely on the temperature of the water.

What you (and many of us) need are sufficiently heavy weights attached to the bottom of the curtain. Also, the outside curtain and anything else that will buffer the pressure differential. Just find a curtain that is strong enough to support the addition of some weights--say, fishing weights--to the bottom of the curtain. Magnets perform better or worse depending upon the construction of the tub. Although if you want to get medieval on its ass, you might get some rare earth magnents from Wonder Magnets. (Which I have, and they're damn fun to play with.)

Velcro is actually a pretty good idea, except you'd want to reinforce the curtain where you attach (I'd say, glue and sew) the velcro. Or just be really carefull. Or, attach some kind of handle on the user side where the velcro is attached to the curtain to use to detach the velcro (instead of pulling on the curtain).

I use one of those typical flow-reducing stainless-steel soap-valved shower heads (and I love it) but the curtain still billows.

You volunteering, trondant and/or matildaben? *winks*

But seriously, I'm thinking weights against the curtain are the way to go. I hate mouldy shower curtains and have yet to find a fabric one that fails to offend my sensibilities, and so tend not to buy ones that could sustain serious weight. I rent, so velcro, as appealing as it is, is probably not practical. I'll go with the rocks, combined with the del Toro/Oldman/Nick Cave/Iggy Pop/Zack_Replica shower curtain.

Thanks, bunnies! I'll report back on the results. Also, thanks for the explanation. I used to be good at physics (before I engaged in dedicated brain-cell-destroying) and figured it had something to do with that, but it's good to know for sure.

I LOVE having a shower that can double as riot control.

This is an excellent personal ad headline.