The bandeau is actually a fairly popular swimwear top as of 2008. In its basic form it's a single strip of fabric that covers the breasts at the front and tapers to about 1" at the back. This style looks okay on smaller chested women but does tend to minimize the breasts; this is certainly fine if you're trying to achieve a boyish look, though. Over larger breasts it can look a little weird if it doesn't fit right, though it does apparently stay up better. At any rate it's not a good idea to actually go swimming in one.

Of course, there's plenty of room for variaton on the basic style. The middle front can be curved inward a bit, giving the boobs less space to wander and locking in a more rounded look. Or even better, the front can be split and fastened back together with a large O-ring or drawstring, and adding straps from this center point. This gathers the two sides into more of a cup shape, making them slightly more supportive. Though still probably not the most stable top, it's very cute and has been quite popular as of late.

A proper bandeau goes down to the empire line, which is actually a really good anchor point for any bust size. Basing a one-piece maillot on the empire line and giving it a halter neck makes for a very stable swimsuit that accentuates the breasts. The bandeau isn't as stable, though, as it has hardly any tension on the top or bottom to keep it in place.

A good deal of the animosity towards the bandeau (at least from the female side) probably comes from poor design: many inexpensive bandeaus have unnecessary boning on the sides, or darts under the bust. These are good design paradigms on other types of swimwear, but tend to make things worse for the bandeau. So, shop carefully and try your best to find a good fit.