So far this is the best new feature of WP8 for me. The predictive words are fantastic and if it doesn't show up, after I type a letter or two it usually shows up. Makes typing so much faster. Good work microsoft!
I love my HD7 and the predictive text. MS really did a fantastic job with it! I use Android and the predictive text is more of a nuisance than anything. And iOS... Don't get me started, it just won't take a hint that I know the word I want to type better than it. WP does a great job suggesting words, including new proper nouns like, well, "iOS", "Apple" and "Android"! However when I type "windows" it does not give the suggestion for "Windows"... Have some confidence Microsoft!
It also seems to do a great job learning what words you type together, or the algorithms are just that intuitive that it knows! And it's very easy to type a word that is spelled "wrong" without it trying to correct you every time you type it (grrr iOS!).