Laurence
I just came across your post doign a search for something else. To answer one of your questions:
If you have a series of old urls which redirect to the home page using 302 redirects, it should have very little impact on the ranking of the home page, because it is the Url of the redirect destination that gets indexed, not the source, particularly when doing on-domain redirects (ie, the destination page is on the same domain as the referring page)
Matt Cutt's google blog has a good coverage of the 302 redirects:
http://www.mattcutts.com/blog/seo-advice-discussing-302-redirects/
Duplicate content means two urls returning exactly the same page, it's more likely that you have a duplicate content problem in that domain.com/, domain.com/default.aspx and domain.com/home.aspx , domain.com/home/tabid/36/default.aspx and finally domain.com?default.aspx?tabid=36 on a DNN site all return the same content. Having domain.com/products/no-longer-available.aspx do a 302 redirect to domain.com isn't likely to give you duplicate content problems (because the destination page is the one indexed, not the source page).
Now, having said all that, what you really want for your deleted pages is a permanent 301 redirect to the most suitable location (this may or may not be the home page). A 301 redirect will tell Google (and others) that the page / product / whatever has been removed permanently, and give a new location to index for that Url. If you have a page domain.com/Products/My_Exciting_Product.aspx, and after a while you find the product is not selling, and decide to delete it, then you should put a 301 redirect in to point any traffic (not just search engines) to domain.com/Products.aspx or something similar. I wouldn't ever return a 404 for somethign that has been indexed by a search engine - you're just throwing away rankings. Much better to 301 redirect that towards another page and help build rankings for the destination page.
The Plug: I've developed a DotNetNuke module called Url Master, which allows you to define 301 redirects for deleted Urls. You just select the page you'd like to act as a destination, and you define any Urls that should be 301 redirected to it. You can download a trial version here : http://www.iFinity.com.au/Products/Free_Downloads/#Url_Master
As an example: you've got a page called products.aspx, and you've deleted a couple of old pages. For products.aspx, you define a couple of 301 redirects:
- products/My_old_Product.aspx
- products/My_other_old_Product.aspx
...and so on. Now, if anyone (including a search engine bot) hits products/My_old_Product.aspx, they will receive a 301 permanent redirect to /products.aspx. Any external links pointing toward products/My_old_Product.aspx will now count towards the link total for products.aspx. Anyone clicking on the product link will still get to your page, and everyone will be happy.
Of course, there are many, many other features in the module, including a 301 redirect to your preferred domain (www vs no www), a 301 redirect from the site root to the /home.aspx page (to stop duplicate content as mentioned above), friendly Urls - this list is far too long to repeat on this post.
HTH
-Bruce