Hello,
I just got my PRS950 for christmass and have been reading scanned PDFs since quite heavily with good results.
To make the reading experience better I use the
free Briss program that allows me to "cut" the unused space along the scanned pages (soPDF can achieve the same for normal pdfs).
As for the quality of the display (e.g. for zoomed books) it looks good (depends of course on the quality of the scanned book!).
If you asked me between an iPad/tablet and the eBook reader I'll go for the eBook reader (if the main use was going to be for reading!!)