I shoot real estate as well. getting the flash units placed correctly is probably the only thing that can be difficult (other than knowing what the agents expect as far as types of shots, but you get used to that really quickly).
Few of things I've found:
1) Shoot your flash on manual, and whatever setting you think is right, you probably want to go down one step on your flash from that. I can count on one hand the number of times I thought "man, my flash wasn't bright enough for this shot."
2) A lot of times HDR, or even just shooting exposure bracketing and using a layer mask takes care of it. On particularly difficult to light rooms, (oddly shaped, large contrast in tones of walls, etc) I'll usually shoot one with the flash pretty bright, one with the flash powered way down, and one with no flash. Then blend these in using a layer mask brush in photoshop (I usually take the two flashed images, blend those together, and then save that image, and blend in the unflashed images to get out those last few unsightly areas). Now this can be a bit time consuming,especially as you learn the technique at first. So I don't do this on all my shots, but usually only the nicest properties. It also depends on how you get paid. I get paid a bit more for higher end properties with more rooms, so I feel a bit of a need to do a better job on those. Which more often than not means more time in post and more time setting up lights (taking multiple shots takes just a matter of minutes total, but setting up multiple shots can easily add 30 minutes to your shoot, especially on a large property.
3) Gotta get your flash off camera and bounce it. With a small softbox (I usually think even the tiniest softboxes work better than the plastic dome covers for real estate work). I also usually try to bounce off the most matte surfaces I can find. Those cabinets seem really reflective, you'd never want your flash point at them, or if you had to, you'd want the flash pointing at them at a very oblique angle.
4) Turn on every light you can find in the house. THe one caveat being if they have different types of lights (ie some tungsten, some (crap, can't think of the blue tinted one)). Usually my agents are super picky about making sure all of the light bulbs give off the same light (makes a huge difference when showing the house to have consistent lighting, they're nazis about this, but some agents aren't). You want to use your flash only when you have to, and when you have to, you want it to make up as little of the lighting equation as possible.
5) Clamps that you can attach your flash to are all kinds of awesome. I believe they are called justin clamps, though when looking for them you find them go by a variety of names. They're essentially just little clamshell clamps with a stud on one side that you can attach your pocket wizard receiver and flash. You want your flash to come down on the image as much as possible, in most situations. If you can find something to clamp onto up high, you get a lot more control of your flash. If you have to flash from down low, you're stuck bouncing it in a very limited number of ways. On one recent shoot, I was able to clamp my light about a foot away from a corner that was just out of view. I then bounced the light right into that corner and got this perfectly awesome spread of light.
6) flash dropoff enhances a sense of depth. When I first started, I tended to want to light everything so perfectly even. However, one of the agents showed me a picture they saw in a competitor's site, and was like "how can we get that shot where the den just looks massive. What i realized was missing was that while I was shooting a really wide angle, the perfectly even lit interiors were sort of compressing things back to 'normal'. If you want to show a huge sense of depth, try letting the lighting fall off in the far ends of the picture. In some ways it's almost a bit dishonest, because when you combine it with a wide angle lens, you can make a mid sized room look cavernous. But my job is to give the agents pictures that get people to actually view the house, so it is what it is.
7) Gels are invaluable as well. If the natural light is very tinted blue or yellow, a light gel on your softbox or flash allows you to more easily correct it in post. You can run into all sorts of problems if you have two different tints of light, because as you fix one, the other gets worse. If you get this wrong on location, you'll probably need to do layer masks with different white balance corrections in post, which is A) really time consuming to get right and B) even when you get it right, it still looks off.
edit: Also, you gotta get those dish towels off the appliances. Totally detracting. And I'd probably clone out the plug on the lamp, if not flat out crop it out.