whether to use a trailing slash in urls or not

I recently switched to mod rewriting of my urls so that I don’t have to show variables in the user’s browser url bar anymore and the url looks more natural to visitors as well as search engines.

One example would be:
http://www.mydomain/blog

This is rewritten as:
http://www.mydomain/index.php?p=bl

To be sure that no incoming links are wasted because of mistakes (if people link to my site I can ask them to use a trailing slash or not but of course they’re will be mistakes at some point), I also configured my .htaccess file so that:
http://www.mydomain/blog/ (thus with the trailing slash)

is also rewritten as:
http://www.mydomain/index.php?p=bl

My question now is whether this could harm my rankings in search engines because now for example google might think that I have two pages on my site which are exactly the same (since with and without the trailing slash might be perceived as two pages while in fact it always points to the same page). Is my current approach (allowing both, with and without the slash) going to get me into trouble?

Furthermore, I was wondering what would be the best way to link to this specific page. Would it be better to build incoming links with:
http://www.mydomain/blog
or with:
http://www.mydomain/blog/

I figure that it would be make sense to be consistent and ask every link partner to do it in the same way (so either with or without the trailing slash for every single link exchange) but is one of the two options more favorable than the other?

Thanks!