This guy had an interesting question (well, ok, it's kind of mundane, but I'd thought about it recently) would you switch from Google if a better search engine came along?
Sure, if Google were *only* a search engine, I'd probably switch. However, I'm using it for more and more stuff. I use it for my primary non-work email, for calendaring, IM chat, blogging, RSS feed aggregator, the searchbar, and (obviously) the general search engine. So, they've built up enough collateral that I'd need a large jump in search improvement (like 10X better, or natural language processing) to switch.
Plus, I like the way Google does things. For one, their products/services just work. And secondly, they use open standards for their implementation. Which means, I can use their IM chat server with any client (doesn't have to be GTalk), I can read my GMail with whatever client I want (they just added an IMAP interface), and their calendar works with ical format, so I can use it to consolidate my work calendar with home. So, even if I want to move away from Google search, I know I can still use their other services because they don't lock anyone out of using their stuff via proprietary interfaces.