permalinks-- what's the max length you try to stay under for the url?

if you run blog.com, I'm referring to blog.com/this-is-an-entry-to-my-blog/

how long do you try to restrict the "virtual" directory part of the url?

google loves blogs, and that's pretty obvious, but a lot of permalinks look incredibly unnatural to me.

are there any guidelines you follow when deciding how you're going to structure your permalinks?

 

my title doesn't have much keyword...i prefer catchy one.