I was in the same situation 2 years ago.
I have a small commercial mowing operation, and 2 years ago I finally decided to go the zero-turn route.
Being that everything I own is diesel, including my wife's VW New Beetle, I was quite hung up on a diesel zero-turn myself.
I've had nothing but Deere equipment since I can remember. Also, living in a very rural area, my Deere dealer is the closest (30 miles away).
For my first zero-turn, the 997 was just way too much - too big, too heavy, and of course, too expensive. I researched the Kubota diesel, and looked like the right size setup for me. But, the nearest Kubota dealer is 60 miles each way, plus I have no experience with them. My Deere dealer has always come through for me if I ever have a problem during mowing season.
So, they had a 727A zero-turn demo machine, which I brought home to try out for a few days. This one has a Kawasaki vertical shaft 23hp with 54" deck. A little smaller than I would have liked, but they gave me a deal on it I couldn't refuse to keep it.
Still not a diesel - it did take me a long time adjusting to running a gas engine for sure.
Went through the last season with that machine, and really got to love it. Small and nimble, and seemed to have plenty of power for my uses.
I am now negotiating to trade that in on a 757 (horizontal shaft Kawi 25hp w/60" deck). The new 2008 line of zero-turns is coming out this month, so I figured I could get a deal on one of their 757's since they are now out dated. I've heard nothing but good reviews on the 757 - plus it is a tried and true machine. I surely would not want one of the new 2008's as this is their first production year.
So, yes, still a slight bit disappointed on not having a diesel for my zero-turn, but these Kawaski engines seem to really put out the power, and have a great history. Sure, the Kawasaki might have to be rebuilt by ~1000 hours, but I usually trade every 2 years, so that is not a concern.