I just buy one set of books. I expect my fellow gamers to own their own sets. I don't think that's an unreasonable expectation, especially since the books are only twenty books each at Amazon.
It just helps if everyone has their own set, so everyone can look up rules or help answer questions about spells and whatnot.
Whoa, wait a minute. I think this is less of a requirement for 4E than it is for 3E. In 3E, everyone needed their own book because of the constant rules references: how does Grapple work? What does that spell do? What kind of bonus is this; does it stack with that other kind of bonus? Spells were the biggest problem--each caster *definitely* needed his own book, and everyone else had to twiddle thumbs after each 10 minute adventuring "day" as the casters looked up and picked new spells.
In 4e, you pick your powers when you levelup and off you go. Assuming you do a decent job copying your powers onto your character sheet, you don't really need to look up anything in the PHB during play--not even the wizards or clerics. The DM, too, has all the needed info contained in his monster stat blocks.
I *just* had this epiphany. No more debate over a half-remembered spell, ending in the DM handing a PHB to a player and saying "okay, look up the spell while the rest of us continue". No more flipping through the MM to look up what's all included with the "celestial" creature type (*how* exactly does smite evil work, again?). It's all right there on the sheet.
Didn't mean to detail into a pro-4E revelation, but holy cow--just the lack of page-flipping alone is a huge boost to speed of play. Less time rules-referencing, more time getting into the game.
