Undestand everybody that I have a Nikon D-300 ($1800) in a Seatool Case with Inon magnifier ($3800) and two (2) Inon Z-240 strobes ($1700). Of course I have Stix arms and UCLS clamps and a Seatool tray ($400).
I usually shoot an Nikon Af-105-VR ($900) in a Seatool port ($400) and use a subsee +10 diopter ($500) and a FIx targeting light ($400).
Alternately I use a Nikon 12/24 ($900)........well you get the idea!
I also spent two years, and still have an Olympus 5050 and Inon D-180 which was the hot P&S setup of several years ago.
I repeat, I am impressed with the Pt-e06 and E-620.
If you want a 5x7 or 8x10 picture for your wall or you want a 640 x480 pixel image for the web you will trim off 1/3 of a Nikon or Canon 3:2 system. Ths the Olympus 4:3 system doesn't really give up much due to sensor size but is huge compared to any P&S camera.
It is true that Olympus does NOT have a lens that is equivilent to my Nikon Af-105-VR. I love this lens because it gives me ultra-fast focus and 8" working distance for a 1:1 shot. However, many Nikon shooters prefer the Nikon 60MM or 85MM for macro because it is easier and the Olympus 50mm compares very favorably with these lenses.
On the wide side most Nikon/Canon shooters like the Tonika 10/17 fisheye in a dome which is no better (nor more expensive) than the Olympus (7/14) in a dome.
In the general purpose area, neither Nikon nor Canon make as good a lens as the Sigma 17/70. The Sigma focuses very closely at a 1:2.3 magnification. While this isn't in the league of a 1:1 macro lens it is quite good. The Olympus 14/54 has specs that are almost as good.
So in general, for underwater, I see only the Af-105-VR and the 100mm Canon lens as lenses that Olympus can't match. In contrast, the Olympus Live view is semi useful underwater while the Nikon is not.
It is true, as Backscatter pointed out, that a dSLR is a step up in size and complication from a prosumer dSLR like a G11. I am not saying don't buy a G11. I am saying take a long look at an e620 rig if the size and complication is something you can handle.
Regards,