Hi Latinandgreek,
I was in a similar position to you, and will need my reader for a lot of pdfs - I eventually decided to go for the PB903, in spite of all the negative comments. In my case it was because I get the feeling that the average PB user is possibly more demanding than average (after all, the unique selling point of PB devices is their flexibility and the constant software development, as far as I can see), and I read many of the negative comments as having to do with the "missed opportunity" that the new PB models seem to be: great hardware, but with software still very wanting.
Of course, it could be that a proper software never gets properly developed (see frequent complaints re PB302 software that never was), but I am betting on the geeks on this forum to actually do something about it, if PB doesn't, and on their generosity in sharing their acheivements with us computer fools
As far as I can tell, Kindle DX is nowhere near the PB903 capabilities even on silly things, e.g. you would have to convert the non kindle formats in order to read them on your kindle, and in general PB devices can be customised each and every way you want - though the new models are not there yet.
Had I not been in a hurry, I would have waited a little bit longer before ordering the PB903, to see how things pan out - but I wouldn't have committed to another device, as from my (limited) understanding PB903 could really be great.