I get most ebooks from Amazon (including free Amazon ebooks). I download them using Kindle for PC, then remove DRM protection using a Calibre plug-in, and then transfer to one of my Kindles or my Sony Reader. Thus I know that I won't lose any of my ebooks and I will be able to read my ebooks on any device in the future.

I'm not sure about iBooks, but I don't see many problem removing DRM from .AZW and .EPUB ebooks from Amazon, Barnes and Noble now that we have great and free Calibre DRM removal plug-ins.

There are much more problems converting PDF ebooks, since there are different kind of DRM protection. While you should be able to remove DRM from Adobe Digital Editions .PDF files, there can be problems with PDF ebooks using other protection mechanisms. Also I don't like PDF files, because it is more difficult to convert them.