Here are my general thoughts on the issue.
1. Don't get an ebook reader to read PDFs... particularly technical PDFs. If the PDF itself doesn't support reflow, it doesn't matter if the reader does. Maybe a Kindle DX has a screen large enough to get away with it... but I think the best place to read PDFs is on a computer or printed out on paper.
2. If you plan on buying a lot of books, and you don't mind being tied to Amazon, the Kindle is the no brainer here. The only device that even approaches competing with Amazon for ease of buying books and loading them on the reader (Barnes and Noble's Nook) is not available in the UK. Sony's software is generally considered awful. If you do mind being tied to Amazon, then admittedly the Sony becomes a better choice since any book store that sells books with Adobe DRM (Pretty much everyone but Amazon and places like Smashwords that don't do DRM at all) can be used to buy books.
3. Battery Life... its a wash.. or close enough not to really matter. Early reports suggest that the Sony will definitely last more than a week on a single charge.
4. Price is a big issue. I think it comes down to how you value other factors. Sony readers have generally (except for fuzzy touch screens which now appear to have been resolved) been the gold standard of ebook readers from a hardware point of view. My Wife's PRS-505 is a quality piece of equipment and I hope it will serve us for years to come. This is not to trash the Kindle, but I will tell you this, there is definitely a different feel in picking up a metal shelled reader versus a plastic shelled one. On the flip side, Sony appears to have decided it is not worth their time to upgrade the software on older readers. They did update the PRS-505 to allow it to work with ADE, they did not update the PRS-505/300/600/700 to support full justification. In contrast, we know that Amazon does indeed push out firmware upgrades for the Kindle. So pick your poison
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Bill