In my opinion, it is a BIG ISSUE - the URL issues of DotNetNuke is so ugly due to SEO. For example:

1) It always included lots of meaningless parameters in the url.

http://domain.com/products/tabid/xx/catid/yyy/default.aspx
http://domain.com/products/catid/yyy/default.aspx?tabid=xxx

2) It accepted unlimited urls for the same page.

http://www.dnnsoftware.com/Community/Community-Exchange/xxxx.aspx
http://www.dnnsoftware.com/Community/Community-Exchange/yyyyy.aspx
http://www.dnnsoftware.com/Community/Community-Exchange/ddddd.aspx
http://www.dnnsoftware.com/Community/Community-Exchange/uuuuuu.aspx

It did not throw any 404 but only be accessed. It looks so strange.

Regards
Baldwin