23andMe is not just a genealogical and health testing firm. It was founded as a research project. They are experimenting with web-based techniques for research on genetic causes of disease. This has the potential of involving many more participants at a low cost and accelerating discoveries.
If you grant them permission, they will let researchers use your data, after it has been scrubbed of personally identifiable data. The firm was founded to find a cure for Parkinson's disease. This paper deals with late-onset Parkinson's. It is a little heavy, but you can still get an idea of what they are doing:
It is well-worth $99 to get the health information and matches with close relatives (Relative Finder), although RF is a bit clunky.However, the raw data can be uploaded to FTDNA's Family Finder, which has much better genealogical tools. The cost is $89 normally, but is on sale for $49 for a limited time only. Note that it is cheaper to do it this way than to buy the FF directly ($269)
AncestryDNA is probably the best of the three for genealogical purposes. (Neither it nor FTDNA give any health information.) it has a database almost as large as 23ndMe's, but the response rate for sharing invitations is much higher.