Best practices for permalink structures?

I get the feeling that I need to change the way I do my permalinks in my wordpress installation. Currently, I just use %postname% which provides for pretty structures with my pages (a good thing) but makes duplication of names in my blog posts problematic. Also, longer titles, such as this post’s, cause a bit of an unruly URL to result. Then again, it is more descriptive than the default which just spits out a post or page number.

There certainly are plugins available to migrate a permalink structure which would be useful were I to change mine. This website claims the best permalink structure is a “blog/category/postname” hierarchy. I definately like the use of the “blog” part of that permalink structure in that it separates off posts from pages (at least that’s what I would assume it does…). People on this forum seem to think that using a “category/postname” or “postname” structure will significantly slow down your database. The WordPress Codex states that using only “postname” has the potential to screw up things within WordPress although there is a note that questions if this is still true in 2.0+ versions.

It seems that there are a whole bunch of opinions out there. I wonder which is the best and most relevant for my website’s situation.