I apologize for the length of time that I haven't posted. I have been knee-deep in work from my summer class and my part-time job.
I recently purchased the newest Tau codex, and I ran the exact same list from the old codex with the addition of 6 more Fire Warriors. The codex works practically the exact same. There are some differences in point values, number of shots, and varied rules modifications to bring the codex into 6e land.
If you liked the Tau in the old codex, the new codex offers a wide variety of new options and improves many of the units themselves. I really want to put a Riptide on the field, but that requires money :p. I have been teaching a friend the ropes on 6e with his Tyranids, so I have been getting a sense of how they work in 6e. They definitely got an improvement overall, but I think that there are just too many units that have no real effective purpose in 6e.
I hope to get more posts in here soon, but that process has been very slow. Bear with me!