Huh, that's interesting. I always wondered why no one is actually building something really really useful on top of this, or is someone doing that? It is actually a nice way of keeping certain records or being able to verify the integrity of documents at a later point in time!
#1 its costly - you have to mine the block AFAIK.
#2 the blockchain is big allready and there will be updates to "skip blocks" in order to keep the size in check.
#3 its very little data
all in all its cheaper, faster and easier to use redundant servers. Its probably more secure as well.