Why are my auto-complete suggestions so bad?

When I'm typing into a text entry field, the auto-complete suggestions I get are much worse than they used to be (they have never worked well on this phone, but have worked great on previous Android phones). For example, if I enter "Th", my suggestions are "Rh" and "Therock", rather than "The". The only suggestions that seem valid are names out of my address book. Any ideas? I've turned on all the auto-complete settings, but the suggestions are still terrible. I'm using a Nexus One running 2.3.4.