For a long time we at Nimblefish had our own marketing automation platform. We eventually abandoned it in favor of Eloqua, but here's a useful feature from that platform that I miss.
I would like to be able to flag certain contacts as test contacts. You could send emails to these records while testing an email, or a campaign, but reports would by default exclude these records. That way your reports would not be "polluted" by test records unless you chose to include them. You could also continue to use test records once a campaign went live, and it would still be easy to get accurate reports.
There are ways to do similar things using list or segment excludes in reporting, but it would be nice to have this built in to the product at the contact attribute level.