There are some great websites developed around good key word domain names. I've mentioned how I am often disappointed when I see a great domain name with a parking page, even though I utilize parking services myself. It's like having a great business location, but the building is empty. I realize it's an investment for the future and parking can pay well, so I'm not looking for arguments here. But even more disappointing than a parked page is a good domain that is hosting a poorly designed site.
At least with a parked page, you know that there is great potential ahead for this domain, that in the right hands, it could be something phenomenal. However, when you see a poorly designed site hosted on a good domain, it just doesn't sit well. It's like driving through a neighborhood of expensive homes and seeing a shack amongst the mansions. A Lamborghini with a Kia engine.
A came across a couple of sites like this. A good example is Guitars.com, a guitar store located in Tennessee. I have no idea what the traffic or volume of business this site does, but the site ain't pretty. This may be the most popular site in the world for guitar enthusiast for all I know, but as a casual viewer, I would quickly look for a more professionally designed site to conduct business with. The design resembles that of something created in the mid to late 90's. Because of that, I think it loses some credibility. Compare this now to guitarcenter.com, a good name, but not as good as guitars.com, yet a far better website.
Another example is haircut.com. This is a great name, in use by a company selling Flowbee and Robocut products. This is a very poorly designed site yet an excellent domain. Again, I have no clue as to how successful the site is, but I can promise you that sales would increase with a more professionally designed site. It also has a retro design look to it. The site goes back to Jan 25, 1999 on archive.org, yet the design hasn't changed much in 10 years.
So keep in mind that owning a great domain can do amazing things for you, but be good to your visitors and give them something pleasant to look at.