Hi there
I recently bought a PRS700 from B&H. Definitely recommended! The whole experience was very good. Emails were answered within 24 hrs (probably would have been even faster if I were not so far away time-zone wise). To top it all off I was lucky, there were no import duties to pay!
Regarding online ebook retailers: I have bought from ereader.com, fictionwise.com, sony ereader store and once from Baen.
Ereader books (bought for reading on my iPhone) are in PDB format. I strip the DRM (can I admit to that without being banned?), then convert the file to LRF via calibre. Fictionwise books can be bought as multiformat or mobiread formats. Mobiread formatted books also need the DRM stripped then converted but so far I haven't had any experience with them as I haven't bought any mobiread formatted books. Baen sells them in multiformats but they are mostly SF/Fantasy books.
When buying books that have geographical restrictions, I can recommend you read the thread quoted by wallcraft. Good tips. The only problem I had was with the Sony Book Store. Although I used my US addresss (more correctly, my cousin's address), my Malaysian-based credit card was rejected. Eventually I managed to circumvent that hick-up by using an entropay.com issued debit card. I believe these cards are non-country specific cards.
There seems to be so many hoops that one has to traverse, but for me, it is still worth the effort. The books I buy (mostly SF/Fantasy/Technical) are difficult to find locally, usually more expensive and take a long time to arrive if ordered through Amazon. Plus I save trees when buying ebooks
Hope this helps.
PK