My experience with this (as limited as it may be), is having a very relative keyword in your domain name is essential for turning up in the search engines. I think it helps people to remember your site's name too.

However, branded names that are off the wall are fun to work with and once you start ranking well for something, word of mouth and media networking will get you going quite handsomely.

An example of a site name that's totally off topic to it's content is TheOnion.com.

Onions really do not have anything in common with the site's categories of:
(as google indexes the site)
Sports
Video
Entertainment Politics
Local
Celebrity Launches Own-Breasts ...
More results from theonion.com »

The site is successful and has a huge readership. So, it goes to show, you just may be able to make a silk purse from a sow's ear!