There are a number of things you can do:
1. Legal: pursue copyright violators, possible DMCA claims against those who circumvent your protection scheme (if you have one)
2. Technical: build in DRM. If not, at least add forensic marking to allow you to track the source of your piracy to know if it's hurting actual sales or not
3. Social: stop propagating the meme that copying commercial data is ok because you are knowledgable enough to do so and it doesn't hurt anyone.
The RIAA has an uphill battle because of no option #2. (CDs have no DRM, despite efforts to retrofit it). They are trying #1 and #3.
Also, I have a counter-example to Felten's claims that DRM never prevented piracy. With BD+ (Blu-ray), we have had some discs survive 60 days before they were cracked. In that time period, there were no high-def rips available on Bittorrent of those movies.
While there are still no large studies showing how many potential pirates purchased a disc due to the delay in availability, I wholeheartedly disagree with "There's nothing I can do about piracy".