There have been lots of threads about steam ovens from owners.

Here's a general search

They are great for reheating room or fridge temperature items (I find it typically takes about 15 minutes -- longer than a microwave but gives better results). Plllog discussed the Gagg's reheating (they call it 'regeneration') here last year. More recently, I discussed my reheating experiences here. Also see this disucssion.

We've only had ours for 2 months but it's the most used oven in our kitchen (out of 4, counting the microwave). We no longer reheat in the microwave at all. As others have found, we use ours far more often that we suspected (having it plumbed in is very nice, I don't know if we'd use it so much if we had to fill a reservoir). We often wish both our wall ovens were steam ovens and find that we'll often use it to do things we used to use the stove for. We have a 6-burner stove, but knowing what we do now, we might have gone for a 4-burner plus griddle or grill given the offloading of tasks to the steam oven.

Other than verifying that mine (old model Gaggenau demo unit) works by firing it up on my shop work bench and steaming some veggies, I haven't got to use it yet.

My understanding of what is on the U.S. market (all 24", but wider trim model is available on at least some models, with identical chamber size):

Gaggenau: steam, convection, or both over a wide range of temperatures. Plumbed into water source and drain. Can select level of moisture at convection temperatures. Door opens to the side (right and left handed models, cannot be swapped). Temperature probe.

Thermador (same company): Similar features, but I don't think that a plumbed version is available. IIRC, the moisture level at higher temps is just ON or OFF. Door opens downward.

Miele: As far as I know, the U.S. models are just steam ovens, so this can't function as a higher temperature convection or combi oven; I think they have combi models in Europe, one of which is supposed to come to the U.S. Water tank, not plumbed. Door opens downward.

Wolf: Seems full function like Gaggenau, including temperature probe, but not plumbed (water tank). Door opens downward.

If you just want a small oven that can steam, and is also an oven, and is also a microwave, Sharp makes their Supersteam products that sell for maybe $600 on Amazon.

Maybe someone else will jump in here and correct any errors.