If you watch the BUILD keynote, you'll see a video of the Word Flow keyboard (however they're going to spell it) being timed by Guinness for the world record, and getting it.
World flow is awesome no doubt but I will believe it when it learns my words using my thumbs. It surely will be my preferred mode of typing considering I never cared about Swype.
I've never used Swype, since I've never used an Android, so WP already has the best keyboard I've ever used, but it definitely has gotten better with this. Can't wait to try it.
Then you have never used a real keyboard! ;-) But seriously, WP's keyboard is almost on par with Android's, except for Android's sliding feature. So this addition should make it pretty much as good.