in reference to the TTJJ hand:
don't quote me on this, but i think you flop a set with a double paired hand about 30% of the time, if i recall correctly. so hands like TTJJ are great for set value, especially if they are suited and can flop you a flush draw as well. hands like 4455 look good i guess but they're pretty troublesome because you are never going to make top set on a board which cannot have a straight (77 is the lowest pair you can flop top set with without it being possible for anyone to have a straight) and they are crushed as a straight draw hand by 3456, 4567, 5678 etc or even 3457,2456, you get the picture.