I use my netbook (has an 160 gb HD drive) as a portable library right now with Calibre as the main software. As it comes with an Atom processor and 1 gb of memory, it handles Calibre and even conversions really well. I have the content server on all the time and serve the epub books to my iPod whenever I want to read one. As the books are about the only files I am storing on this device (except mails and temp files), there are a LOT on there (I got a backup, too of course
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It just is the IDEAL solution for this purpose combined with Calibre and some additional converter tools. I can handle any files thrown at me and convert them into ePubs really fast, check and edit the meta data and even read the occasional ebook on it.
I use it to "feed" my (oh well, my wife's) Cybook and my iPod and download the books I want. The best thing for me is the fact that Calibre never has slowed down a iota even with all those books it has to manage.
@monty: My netbook has a wide 9" screen. I like that form factor!