Is it still worthwhile nowadays to create a mailing list to keep your customers updated with product news? Since you can achieve the same with Twitter follows and Facebook page.
If your email has something interesting to say, then absolutely it's still worthwhile. It seems to be a growing area, at least from my perspective. It probably depends on the product, but most likely you'll get some value out of an email newsletter.
I think the number of sites which still use mailing lists pretty much answers this question. If in doubt, follow the crowd. Depending on your users, you probably shouldn't assume they will be using Twitter / Facebook to keep on top of updates.