Do the search engines (most importantly google) give preference to where the keywords are located in a URL?...

eg... for the keyword widgets...

is widgets-blue.com better than blue-widgets.com ?
is widgets-blue.com or blue-widgets.com better than widgets.blue.com?
is any of the above better than blue.com/widgets/ ?
and finally is blue.com/widgets-by-frank/
better than blue.com/franks-great-widgets/ ?
Anyway, i'm sure you see what i am getting at... what (if at all) is the hierarchy for URLs?

Thanks in advance,

It does help, but the degree in which it helps is something people tend to disagree on. Use a key word suggestion tool to see which one would get searched for more.

Drowning a SE in hyphens is dangerous (spammy). Also, anyone can make a directory with a keyword in it, so owning a domain with that keyword makes you more unique and is therefore more valuable. SE-friendly url's are a good idea, but don't spend too much time worrying about keyword-stuffing your directories -- your mental energies would be better spent elsewhere.