When you are looking at any cloud solution, this is the first questions you should ask. Can I get my data out? Read Write Web has a story on a new Google tool that allows just that.
ReadWriteWeb: How to Liberate Your Data from Google
It is definitely something you should put some thought into. If the product you are using goes out of business, gets discontinued, costs too much, whatever, can I get my data out? It is one of the reasons I use blogger. Simple interface and good export tools. Makes backing the thing up easy.