Amigos,
I read these threads and want to add my 2 cents............
Even though I am primarily a dSLR shooter I have used (and sold plus coaching people) many Canon G7, G9 and soon Canon G10 underwater systems.
While many want the add on wide angle lenses housing manufacturers are challenged with where a particular lens and body is positioned to try and take advantage of whatever the widest lens angle is and still give users some zoom and macro capability. If they use a flat port, and the lens as Ikelite has recently stated is too far back at the widest position it physically cannot take advantage of ANY external wide angle optic. Then people are dissatisfied 
If a manufacturer gives you a dome port to restore the widest angle view (like the 28mm equivalent film term of the new Canon G10) then at some point the lens will not be able to zoom in and focus or shoot in the best macro range.
I also personally think most P&S shooters (even high end ones like the Canon G7, G9 and G10) ever get close enough with an external wide angle lens. So the difference between shooting tighter framing from say 3' -5 away with the Canon G10's 28mm lens versus a wider lens is lost on 99% of shooters IMHO.
I personally would rather have the 28mm wide view accepting the compromise of 1/2 or a bit more zoom range of a Canon G10 as that is more my style of shooting (Head / Shoulders of divers, coral formations, reef fish, etc.)
I hope to shoot some test shots in Cayman Dec. 6-13th with a Canon G10 underwater............
Just one lowly guy's opinion 
dhaas