This just reminded me of something I did recently with a 301. I had an old site that probably was penalized because of too many spammy links, mass blog commenting, forum profiles etc. I could never get it's rankings out of the shitter. I 301'd that site to another domain that I had sitting around for probably 6 months. The new domain had no content at all. I took all of the content from the original site and dumped it into the new site. Within a couple of weeks the new domain was ranking in the top 15 for most of the keywords that the original site was going for. I built no new backlinks to the new domain either. It ranked strictly off the 301 I'm assuming.
In this situation, was the target/new site hosted on the same IP as the 301'd/penalized site?
Are your rankings still holding?