We did the semi-built-in hybrid similar to what I think cathy725 is describing. We backed into that by accident. Were planning on a built-in and the cabinet is made to the specs for a panasonic built-in, but a month prior to our reno -- per Murphy's law -- our microwave broke. So we got a $99 kenmore to tide us over. Then when we realized this microwave would fit the space nicely and the cabinet has the required clearances for it (the microwave is smallish), we decided it would be better to do the semi built-in option. So we asked our cabinet maker to put a strip of molding at the top to give it the appearance of being more built in, but the interior dimensions are actually larger. We figure this gives us the best of both worlds. Lower up front cost by reusing our existing micro, ease of replacement if it breaks, and the cabinet is still sized for a built in if we ever decide to change our minds on that. But given our experience so far in the 14 months we've had this, I don't see ever switching back to a built in now. Here's what ours looks like. A bit hard to see the molding strip that makes it appear more fit-to-size, but the interior cavity goes up to the bottom of the frameless cabinet door above the cutout. Please forgive this grainy pic that makes the mw look horrible, it's not a high enough photo resolution to be blown up that big, but hopefully it gets the point across:

I'll chime in here. I have had mine in use about 7 1/2 years. They were brand new when we started looking and planning and I had a hard time the the price tag. As it turned out, using the drawer solved a lot of layout issues so we paid the $6-700 it was then, realized it was our east expensive built-in appliance, Sharp makes the best microwave ovens, and we figured the cost should go down by the time we might have to replace it and worst case we could put a small shelf unit in the space. Well, the cost hasn't gone down, I'm sorry to say, but I am not looking to replace it either. When I do, it will be with another drawer. I was pleased with how well we liked using it, found it had settings I didn't know it had and they worked well for us, and the keep warm setting gives me a second warming drawer for the craziest of times (actually used both for Thanksgiving one year when one guest was over an hour late). The drawer opening is so much better than having to bend down to see the flat front of a shelf unit or to reach in under your counter. Not having to lift out a steaming dish, set it down, stir and lift it back is so much easier. I'm tall and have bad discs in my neck, so that matters to me more than our other family members, but I don't think they'd want to change either. I'm coming up on 8 years in and I'm not going back. Point well taken about the cost of a micro plus trim kit of a built-in version that may not need the trim kit. And the only appliance you might get for less is a DW if you go basic. For a better, quieter model, you'll be in the same price range.

I am with you in that I very rarely use my microwave. In fact it broke 2 months ago and it is not an issue, except one time when my husband and I were going out one night and as a treat my kids wanted lean pockets(a forbidden food) for dinner. I baked them in the oven and they were apparently not as good. Have you considered taking the current microwave out now and living without it to see what it feels like? I always only planned to get a tiny microwave, 0.7 or 0.9 cubic feet. Originally I thought about putting it under counter on a shelf in my island, then I decided I didn't want to waste MY island real estate on something I didn't even like. I then changed my plan to put it on an open shelf. I also debated about sticking it in our walk in pantry. Since it is currently broken and not an issue, I am just not thinking about it, and not acting on it. I will have the open shelf made deep enough, 13 or 13.5 inches to accommodate one in the future should I decide to buy one. That's all I am doing. Anyway this is my vote for not kowtowing to the "you must have a microwave" majority.

I have a countertop model microwave on a shelf on the working side of my island. We don't use it all that often so I didn't want it to be more prominent or expensive. I don't really mind the gaps, you just have to clean them out periodically but it's not difficult. (We left extra room on the sides for venting purposes, you don't want a tight fit with a countertop model.) one of the cons that you didn't mention is that it can be difficult to see the numbers/controls when it's at a lower angle. That wasn't something I'd realized until after we made the decision to treat our microwave this way. However, we don't actually find it to be all that inconvenient... it was worse when the microwave was new to us, but we pretty much use the same buttons over and over and you get it memorized quickly and there's no real need to actually see the controls. I'm sure there are others who use their microwaves for more functions, but we are not one of those households so this works very well for us. If I had the chance to do it all over again, I would have still made this decision for microwave style and placement, but I still wanted you to be aware of that additional con. :)