Some of the better questions and answers that came up:
Is there a an SEO advantage for either .NET or php?
Short answer is no. They are both perfectly fine languages and can generate search friendly dynamic content as long as some simple guidelines are followed.
Mod Re-write, or Isapi Rewrite to keep URLs clean, and of course avoid the common mistakes like session id’s multiple URLs for the same content etc.
There was some mild debate on the panel, as Sage mentioned that in his experience, it has been easier to get Mod Re-write accomplished, thus giving php an advantage for him. Because of our development backgrounds, Colton and I have both had relative ease with both .Net and php.
A good question from an attendee: “I have millions of pages and only a small percentage are indexed. Should I use sub domains”?
All panelists seemed to agree that sub domains are not likely to solve the problem. There is likely another core issue, such as session id’s, duplicate content, query strings, etc., to look into first.
It should come down to the user. If there is reason to break it out into many sites, for the users sake, then do so. However, if it makes more sense to have all of the content under one domain for the user, then leave it that way and diagnose the real reason the site isn’t being fully indexed.
A member from the audience did make the point that with a site that large, it may simply be a matter of disc space. He had observed in his own industry, that sites with millions of pages just don’t get fully indexed due to limited resources of the engines.