I've been using Swiftkey X for a few weeks now (thank you 10 cent Market sale) and it tailors itself to your vocabulary pretty well. I hit the 10,000 strokes recorded milestone the other day, even.
Eventually, when you start to type out a certain sentence or phrase regularly, you only have to type in the first word, and the suggestion box will fill pop up with the next word, so I only end up tapping the suggestion 4 or 5 times and finish out the whole sentence. Pretty cool.
Sometimes though, it gets stuck in a conversation with itself. I kept tapping the suggestion to see where it went, and it turned into "when are we going to the to the to the to the..."