I'm a big Fictionwise customer and will continue to be one. I'll simply keep my purchases to non-DRM .PRC titles from now on. I have many DRM .PRC titles and also eReader .PDB titles that will have to be read on my T|X for now. If I really desire a new DRM title I'll look for it on Amazon.
Yes it's a huge pain in the posterior. I remember going through the same mess going from LP to 8-track to cassette to CD. Also VHS (never did Beta) to DVD. It's aggravating and costly for the consumer but at least I had options where I could record from the original media to the newer media, well except for 8-track
Now there is no option except to read on the old system or (when possible) repurchase the books in the new format.
I don't like it but I wanted a eInk device and I like the look of the Kindle and the features. (Yes, I'm in the minority but that retro look appeals to me.)