That's not called lock-in, that's just service. Lock-in would be if they didn't provide an easy way to get your data off, forcing you to continue to use flickr

That's not called lock-in, that's just service. Lock-in would be if they didn't provide an easy way to get your data off, forcing you to continue to use flickr (you're locked in). But they provide a clean API for you to do just that. There are lots of tools you can use to pull your data off easily.