I do Tae Bo a few days a week and I've noticed considerable improvement in
the tone and definition of my thighs, glutes and obliques.  I still go to
Curves 4-6 x a week and have started pushing myself a little harder in that
workout too and don't need a day off in between.  I can do TB two days in a
row, but not three.  If I do my dumbell work (8-10 lb dumbells) I take a day
off in between or do upper body one day and lower the next.  I give my
muscles rest based on when they need it and I generally know when that is -
the workout is either more difficult because I feel less strong or I just
don't feel like doing it which isn't normal for me.

I don't have access to a trainer but I do have friends here who are very
into fitness and exercise and we sort of help each other along.  I know
enough to stop when something doesn't feel right and that's probably helped
keep major injury away, though I do have a seized hip flexor that acts up on
occasion (like the last few weeks) and that mainly restricts my range of
motion until I can get it stretched and massaged back to normal.

All in all I think it boils down to the intensity of your workout.

Jenn