We used Teaching Textbooks 3 last year and did NOT love it at all. There were literally 2 pages of errata that they sent along with the books and CDs, which was ridiculously lame (who sells a product and includes a "PS Here's all the stuff we did wrong with it"?), the content was kind of random, and disc 3 never worked (after 2 phone calls and them telling us it was our PC, they relented and snail-mailed us a new disc 3, then we found discussion forums where many, many other people had the same problem with disc 3).
So for some odd reason I'm considering it for 5th grade math. :) HA! What is wrong with me?!
I did like that my daughter could be self directed on most of it. She didn't complain as much. If we used it again, we'd definitely have to supplement it with more stuff, either free or very low cost. So my main question is, has/does anyone use TT 5? Is it any better or worse than 3 was?