When I'm designing a logo, either for myself or for a client, I use the "less is more" principle.
Sometimes, I find logos are very cluttered and unnecessarily have a lot going on within them.
Well there's nothing necessarily wrong with that, a logo is just a logo at the end of the day.
Something people can use to identify your site/brand with.
However, simple logos are often just as effective at doing that as detailed logos are.
As Mal has put it, some logos are just far far too complicated for their own good and people get lost in a sea of shapes or colours.
Where as, a simple text logo with a simple icon next to it (icon that is relevant to your niche/industry) is all that is required really.
The other thing to consider when designing a logo is, do you require it contain your company name and slogan or just your company name?
Do you want to have your company name as words, within that logo or do you want only an image/icon only?
Do you want a logo that you can use on not just your site but on business cards, leaflets, flyers, letterheads etc?
Example: I've been experimenting with some logos for my coffee body scrub site.
I'll probably go with something simple like this.
The site is about a coffee body scrub so it contains a coffee bean with a crown on it and just my sites name and slogan.
IMHO anything more than this is just unnecessary overkill.