You "should" pass the correct pageid.
Actually the best solution would be to implement friendly urls in the blog that map to the real url with query string params. I plan to implement this in the mojo blog when I get a chance but you could do it in your custom one.
There are already code examples for creating friendly urls as in PageSettings so that part is easy enough. It would require adding a field to the blog table for the url so it can be used in the blog's internal links. So the url could be the title of the blog with spaces replaced by dashes and then removing any non alpha chars besides the dashes. I'd probably lower case it to so it might be like /3rd-skin-of-10-completed.aspx which would map to a real url like /BlogView.aspx?pageid=2&ItemID=358&mid=19
This would make it easier to get the correct url in your blog summary feature as well without having to worry about pageids.
Hope it helps,
Joe