What's the difference between currency and float field types?

I'm looking to setup some fields that would store prices in them (e.g., 46.10) for a custom object—prior to now, I've always used float field types to hold this sort of information. From a structural point of view, are there any advantages/disadvantages to using the currency field type instead? This data would not be displayed in any emails/landing pages/etc., so formatting is less of an issue. Are there any plans to support multiple currencies?