In that case, I definitely recommend a filter over messing with friendly URLs.

The filters are free (to a point), efficient but with full fledge Reg Ex and iterative rules.  They are stable and won't be an issue during DNN upgrades.  I run one site with over 70 rules which I thought would be a performance hit.   I used the good URL rules (above) and the rest are still a fraction of what it takes DNN to run.  The only real issues I have had was with mutli-portals using the same tab paths.  The fix was just a matter of being explicit. 

As to Google PR, if you have a page with +hundred back links, don't move it.  Even a 301 redirect saw a hit in terms of PR and traffic.  Instead, make a copy with enough differences to not be a dup and maintain the page for as long as you own the site.  This assumes you make some kind of money off the page so the effort is worth it.  I recommend duplicating your feeds as well.  I don't trust all readers will update to the new location.

Given a few catchall redirects, all the rest of the blog pages will move in about three weeks without issue.

Oops.  I was trying to make a change to the formatting of the web.config code and the page submitted on me.  I'm actually glad it submitted.  I thought I had lost the post.

Anyway, I was going to say that if you go the custom 404 route, you will want to make sure you still leave a way to return 404 errors for pages that don't fit your pattern.  You would need to make sure that the Response.Status was set appropriately (404 Not Found).

One last thing to note if you use the first approach, a generic 301 redirect for one entire directory to another can be used when the files are all the same (you've just moved a directory to a new location).  When you are moving from one environment to another, like from CommunityServer to DNN (Kudos to Chris on the move, by the way), you'll need to write a little custom code to parse out the old URL and redirect to the new.

HTH,

Don Worthley
IT Crossing