What are the advantages (or dis-) of the GT triple triangle frame?
A significant drawback I've found (I've got one of their hybrids) is reduced options for mounting things:


My toddler seat has to go lower than it otherwise would, making it much harder to fit panniers underneath.
I can't fit a triangular tool bag there
It makes fitting a D-lock mount inside the triangle harder




(obviously these 3 are pretty much mutually exclusive anyway)

Also it makes shouldering the bike harder -- your shoulder is further forward meaning the bike isn't as well balanced.