I come to this thread, like many others, being tired of carting EOS DSLR's to places I don't really need them. I have Canon 1d, 5d and 350d. One alternative is to upgrade my 350d to the current 550d. Another alternative is to go down the G1 route.
Sizewise there is little difference except in the case with the pancake. But it is the weight that is the big difference. On average one is reducing the weight by around 25%.
I may be a bit out on the prices (foregive me) but I think I am accurate on the weights. The three options are listed below:-
Walkabout large aperture
Canon 550 + 35mm f2 £950 640 gms
G1 + 20mm f1.7 £650 485 gms
Kit medium zoom
Canon 550 + 18-55mm f4 £820 740 gms
G1 + 14-45mm f3.5-5.6 £450 575 gms
Wide angle zoom
Canon 550 + 10-22mm f3.5-4.5 £1230 915 gms
G1 + 7-14mm f4 £1200 685 gms
Maybe a 550 is not a good comparison, but I used it as (a) I have something similar and (b) a nearby post mentioned someone who was moving in the reverse direction - namely selling his G kit and moving back to a 550.