Siri is nothing more than a web search engine with a cute, but simple voice front end slapped on. It also serves as an alternate input for mindless tasks such as creating reminders, dialing phone numbers, etc. Watson, on the other hand, is a very complicated artificial intelligence engine that is able to interpret very subtle language cues. For example, it understands "puns" and double meanings in words as well as very complex language structures. Siri isn't even a drop in the bucket compared to Watson. I mean, can you imagine a Jeopardy contest between Siri and Watson? That would be hilarious!