g1smd - 10:16 pm on Mar 2, 2011 (gmt 0)
You must list all the 301 redirects before any of the rewrites. You have a bunch of redirects at the end that should be near the beginning.
The redirects can be much simplified, the first nine condensing to:
RewriteRule ^(category|popular_tags|subscriptions|favorites|disabled)/$ http://example.com/$1 [R=301,L]
RewriteRule ^tags?/$ http://example.com/tags [R=301,L]
RewriteRule ^(webmasters|contact|about)/$ http://example.com/about [R=301,L]