I built my own landing page which links to 6 separate Juicebox galleries - see what I did here:
I've done a very similar thing using TTG CE2 Auto Index for the main page and Juicebox for the galleries. It doesn't achieve the thumbnail gallery idea so much.. but it helps to break large galleries down into much smaller subsets. Just like Michael's example, I used it to break 300+ photos from a wedding into all the different logical groupings: Pre-ceremony, Ceremony, Reception, Family & Friends, The Couple, Food, etc.