It's incomplete: CBS shows? Sorry. Live sports? Nope. And you can forget about Viacom shows such as Comedy Central's popular "The Colbert Report" and "The Daily Show With Jon Stewart." If you want comprehensive programming, Hulu Plus isn't ready for primetime.
Your Internet connection is too slow: Hulu Plus streams in high-def (720p) resolution, but a super-slow broadband link won't cut it. If you need to upgrade to a faster connection to run the service, the added expense will limit the savings associated with canceling cable TV.
You really, really hate commercials: Yes, TV shows on Hulu Plus come with commercials. You can't fast-forward past them either.
Netflix is good enough: Netflix offers video-streaming for $8 a month, and it has a comprehensive catalog of TV shows and movies. Hulu Plus' TV vault is deeper, though.