WPF or WPF/E are too weird and have too many hard syllables. Has anyone found a nickname yet? Or a better way to pronounce them? I suggest "Whippfee" for WPF/E. Makes it sound like an R2 astromech. 
WPF/E will need a better name if Microsoft wants to target it at the standard "everyone" market.
Avalon was a real good name. Everyone took to it quite nicely. If they're worried about trademarks, they wouldn't have a trademark issue if they just make it "Microsoft Avalon(tm)". Like Flash (which is actually "Macromedia Flash"), people will call it just Avalon.
While I don't usually critisize Microsoft, I think they've got this whole naming thing backwards. Me, I would've called it WPF inside the company. Then when released, it should take on the "codename" they usually give. "Codename WPF" sounds better than just WPF, and Microsoft Avalon sounds much better than Microsoft Windows Presentation Foundation.
Sigh. That "official" name has more syllables than the entire works of Shakespear (even the ones that the monkeys wrote). If anyone finds a better name for WPF and WCF, please drop me a line. I'd very much appreciate it.