My wife has a rule--if a book comes into the house, another book has to go out. She spent the first couple of years we were married stopping at every garage sales to see if they had bookcases. Then one day, she realized our house had turned into a library and we still had stacks of books on the floor.
eBooks are the perfect solution--they all fit on your computer hard drive so you never have to buy more bookshelves. Figure that shelf space is worth what, ten dollars a year per inch, and you've cost-justified the three buck eBook penalty.
That said, eBooks shouldn't cost more.
About propriatary formats: my company,
BooksForABuck.com, and Fictionwise's 'multiformat' versions both allow you to download multiple formats, including HTML, which will definitely be around long after your Sony has hit the eBook reader in the sky.
Rob Preece
Publisher,
www.BooksForABuck.com