SourceItem #417 in the "Starcraft Ghost isn't dead yet" files: speaking with MTV, Blizzard's Frank Pearce says that while the company's attention has turned in recent months (well...years) towards some more high-profile titles, Ghost is not, and never was, cancelled:
It never was technically canceled. It's just a focus thing for us right now. We've got a finite amount of development resources and a lot of different things that we want to focus on so there's always the possibility, but right now we're spending our time on "World of Warcraft" and our expansion "Wrath of the Lich King" and "StarCraft II.
So when one or two of those products ship, you can all get back to badgering Blizzard about bringing back Ghost. Or Diablo III. Actually, you'll probably find the time to badger about both.