I have a GE Profile microwave/convection oven combo (NOT the Advantium) but not because I went out of my way to get that. I needed a micro with specific dimensions and features and the one I chose just so happened to also have convection. I've had it for 3 1/2 years and I've been quite happy with it's performance until recently when the magnetron tube crashed on it. That would have been a $275 part but fortunately that part had a 9 year warranty and was covered. I asked the service guys who came out if this was known to happen with this model (a JEB-something, I can't remember the model #) and they said no. Since I've had cheapo microwaves that went on forever 3 1/2 years seemed awfully soon for this to happen.
I would suggest you have a look at the appliance or kitchens forums over on gardenweb if you haven't already as most of the folks over there are in the process of building kitchens or complete homes and will be up on the latest scuttlebut:
When I stand before God at the end of my life, I would hope that I would not have a single bit of talent left and I could say “I used everything you gave me.”