I recently made this same decision b/c I chose the extra counter space over the higher up oven. I am going to go with a dual fuel slide in, most likely a Bosch Integra HD7282U 30" Pro SS with warming drawer. It has one 16K burner too. It was more cost effective and I am getting the warming drawer that came out of the plans early in the process. I need less granite and it is one less cut in the granite. The warming drawer keeps the large oven w/ hidden element from being too close to the floor.
That said, there are combinations of cooktops and wall ovens that will work. Just be very careful to follow the specs of each appliance. Some cooktops are too deep to place an oven below it.

I have my oven under my cooktop and am really happy with it. In the old kitchen, the oven was 'up', and I lost far too much valuable counter space in my small kitchen. Furthermore, whoever was cooking was continually having to move, so that someone else could get at the cupboards below the cooktop, which drove us both crazy.

I think a slide in range would perhaps be less expensive, but I prefer the look of the counter, plus I wanted a 27" oven, beneath a 36" cooktop. It's been ideal for me.

sara--I love that idea. I had been wanting a 36" cooktop but I have very limited room for lower cabinets so I didn't want to eat up that much space. How do the cabinets work with a 36" cooktop and a 27" oven? Do you have the oven centered below the cooktop and then cabinets like normal? Are there special considerations to have cabinets below the cooktop or can pretty much any cabinet go below a cooktop?

Before you go the undercounter oven route, please go to an appliance store or kitchen place and try the undercounter ovens yourself. In general, an oven mounted undercounter will be much closer to the floor than an oven in a range. We originally considered it but when we saw how low the oven would be, we knew it was definitely not for us. When opened, the handle was just an inch or so off the floor! A range has the oven directly under it w/o having to allow extra space for circulation, etc. that you have to have b/w a cooktop & oven, so the oven can be higher off the floor than a separate oven. You also get the added benefit in a range of a storage drawer, a WD, a small second oven, or other configuration.

In the end, we went w/a cooktop w/double wall ovens mounted in a tall oven cabinet. The bottom oven is higher off the ground than an oven in a range. Under the cooktop are cooking utensils in the top drawer and pots & pans used at the cooktop in the bottom two drawers. It's rare that anyone needs something out of one of the drawers when someone is standing in front of the cooktop. (Prep tools are off to the side and the baking utensils are on the baking peninsula.)

Casserole dishes, cake pans, cooling racks, etc. are stored near the ovens (drawer under the ovens & tray storage above the ovens).

eks6426 - my GC said we wouldn't need an actual cabinet to mount the oven in - he built a plinth for all the cabinets to stand on, because our floor isn't level, and this allowed him to level it up. It also meant he could incorporate the correct requirement from the floor for the oven. He mounted a facsia panel, sprayed to match the Ikea cabinets on either side (the colour is exact!) with the opening size cut out. The oven then just slides in.
There is about 3" of facsia panel showing on each side of the oven - we discussed using the space for cookie sheet storage, but eventually found a spot elsewhere that would be easier to fit the door onto (I didn't want pull-outs). My GC suggested - if I wanted to give the impression of a complete range - covering the fascia panel with stainless steel instead, which would make the oven look as wide as the cooktop. It wasn't the look I was going for, so I didn't do it, but it's a good idea if it's what you want.
You do have to check the clearance requirements carefully: he ended up having to raise my counter by an inch, which was disguised with some clever panelling, to get the correct gap under the cooktop (a Bertazzoni). Some cooktops need more than others, so check before you buy!

As it turns out, although I'm 5'3", I really like my higher counter too. I note buehl's point about checking how low the oven door opens: I'm happy with it, but I'd had a similar combination in the UK, so was already accustomed to it. For me, the key was to get more counter, and for anyone in the kitchen to have access to pots, bowls and utensils, without having to shove the cook aside.