That's why, when picking an open service, it's important to look for ones with open APIs so that with a little effort you can get at it. (But not have to stoop to screen-scraping...)

Examples: Flickr, Delicious, etc.

Gmail is a shining example of not locking you in-- they offer to forward your mail for free. They know they're good enough that you'll be there even if you don't have to.