It's a timely warning that just because a service is available, it's not guaranteed to be robust. Beta means that the product is not ready for a full release, and there will be problems. To be relying on a beta product with no personal backup is not a smart thing to do, even though the product looks stable.
On the flipside, neither should a company expect to get away with slapping a beta tag on a product that is not ready for public use. I'm not suggesting that Nokia are doing this (although I could look at some fly by night Web 2.0 companies and wonder) but you still need to be a little less trusting of software with the beta tag.
The use of beta software for critical real world applications has grown in the last few years, and should always come with a warning that anything could happen – for the right to see software early, you are asked to give feedback. And in this case, Nokia have done their side of the bargain and been full and frank with their testers as well.
-- Ewan Spence, Feb 2009.