Does it make any difference to SEO ratings what-so-ever if your url has a trailing slash:
as opposed to one that does not:
Read the full blog post by Google here, http://googlewebmastercentral.blogspot.com/2010/04/to-slash-or-not-to-slash.html, it covers this exact topic.
Long story short Google does not care if you have a trailing slash. However, it will treat the below 2 paths as separate pages.
If you need to have both of the above and they are the same content your best option is to do a 301 Redirect to one of them from the other.
If that isn't an option you will want to add a
In addition to RandomBen's point about search engines treating URLs with a trailing slash versus without as two different URLs, I'd like to add this. I generally use the trailing slash to indicate a category, while I don't use a trailing slash for pages that are at the end or bottom of a hierarchy. Slash your categories, don't slash anything else. If you're rewriting URLs, this most closely matches the natural file structure. However, you should make sure that each category in your path exists, or you could end up with some confused and frustrated users. In your example URL, "some" and "slug" should both be accessible pages.