I have no problem with the size because books are relatively small and I only will be reading one at a time. The rest of the space I would be using for comics (also not a lot at once, just a few to finish, then move on to the next chunk), some of my daily rss feeds to text or pdf. The only stuff I want to store on there on a more permanent basis would be literature regarding my work (computer programming) for reference and any other type of reference books I need.
Just did a little searching on Calibre and other than having an ugly interface it seems to be the de-facto software to use. Just looking around on ebay though it seems all the buy-it-nows are the same as in store or come out to the same or more with shipping. I am lazy and don't like to bid though
I'm thinking I will go with the PRS-300 in the end though. I decided to buy one as soon as I finish this book.