I have two questions:

1. I've always been under the impression that for what Facebook does, a traditional RDBMS simply cannot handle the scale (like, not even close). Is this correct?

2. I'm also under the impression that due to the architecture Facebook runs on, from time to time some lesser-important data (ie: a status update or comment) can be lost (temporarily or permanently) and this is not considered unacceptable. (It seems perfectly reasonable to me for this particular use case.)