When I tell people about Paint.net I would have expected them to use www.paint.net as the way to get the program. I just checked, and see that www.paint.net is a parked domain. That really should at least have a link to the actual web page. In retrospect, I think the idea of using "paint.net" as the product name was not a good one. The name itself is a web page address that is not the real web address.
If the www.paint.net web site is not going to be used, perhaps it would be good to rename the program. Though I do think starting with the world "paint" is a good thing to do; "Paint for You" "Paint World" "Paint Photo" "Paintshop". I know such renaming is going to be painful. There is so much out there that refers to the paint.net. Tutorials etc, that refer to the name, they may never be edited to the refer to a new name. So, that is why I think using the paint.net domain to redirect is the best choice.
-Joe
