San Francisco, CA
Fast Water Heater Company performed installation of our water heater, which was purchased through Home Depot. Overall, it went fine, though was a little pricey.
Contrary to other reviews, Fast did *not* have our Home Depot water heater in stock; they had to make a stop at Home Depot to pick one up. That really didn't affect us; they showed up with the water heater in their truck, just the same.
* the installer appeared to know what he was doing. He even manged to perform the entire installation without an assistant. I was impressed, considering how much that 75-gallon water heater weighed. The installation went smoothly, and in the following months, we haven't had any problems. He mentioned some possible (extra cost) plumbing changes that *might* be necessary, but was reasonable and in the end only one fairly small one was needed.
* The only (small) issue was that he didn't do a thorough check of the system afterwards -- we had no water pressure at a faucet and shower at the far end of the house after the installation. It turned out that there was some sediment, probably from the old water heater, that had flushed through the line and deposited in the screens in the faucet and shower. The installer could have either checked it, or warned us that that could happen and how to correct it. (it was easy to fix ourselves, once we knew what the issue was)
* The cost. The installation cost as much as the water heater! $1400 total, which just blew me away. And ours was a very simple installation -- drive straight into the garage and install -- no stairs, no basement, etc.
$145 of the cost was for a "permit", which seems ridiculous (but was set by the county, not Fast, so I can't blame them for that). The permit $ paid for an inspector to come out a week or two later and spend 2 minutes to say, "yeah, that's up to code", and leave.
Next time, I'd prefer to go through Sears -- which was our top choice in the first place (highly rated Kenmore water heaters). However, our size water heater at Sears was locally out of stock, so it would have taken nearly a week to get it replaced ... and my family wasn't willing to take cold showers for a week ;-).
If you can install your own water heater, go for it. You'll save hundreds of dollars and won't need a permit. Plumbing isn't my forte, so we had to have an installer. Overall, Fast did a good job.