Ok, I implemented better 404 handling (at least for .aspx and files handled by .NET).
I've updated this site with the new code. So for example if someone typos the url to the download page like this
It will go to the 404 and google will suggest the correct download url
If you use Firebug you can see the status is 404.
I have some other things to finish before I can merge this to trunk. Currently its in my sandbox and it will only compile at the moment for MySql because I haven't implemented some new web store methods in MS SQL yet. Should have it in ther by tomorrow night though.
This was a good suggestion, the previous handling of 404s was masking 404s from google for .aspx pages.
Its possible to disable the handler by commenting out the httpmodule in Web.config
<add name="PageNotFoundHandler" type="mojoPortal.Web.PageNotFoundHttpModule, mojoPortal.Web" />
and you can disable the google enhancement by setting this to false in user.config
<add key="EnableGoogle404Enhancement" value="true" />
Its also possible to render a custom 404 page using this setting:
<add key="Custom404Page" value="/PageNotFound.aspx" />
you can put a different .aspx page or even a plain html page.
The built in PageNotFound.aspx is nice because it shows the skin and menu. Seems a pretty good solution.