Using the RSS feeds from your account and a couple of useful websites, it's possible to syndicate and share your Instructables, forum topics, favorites, and all the rest of your activity on Instructables to Facebook or Twitter. This is a great way to share your projects and posts on Instructables.com with friends and family that might be more familiar with Facebook or Twitter.
You can use these same techniques for other sites too, and I'll let others respond in the comments with their favorites.
Once you're syndicating your projects, you might want to follow the featured or recent Instructables on Twitter or Facebook.
Step 1: Find Your Instructables RSS Feeds
The RSS symbol next to a listings of Instructables items is a link to that listing's RSS feed. Copy the URL of the feed.
Step 2: Twitterfeed
Twitterfeed will post multiple RSS feeds to your Twitter account. Create an account, and setup your RSS feeds.
Step 3: RSS Mix
Facebook allows you to import a single RSS feed. When viewing your profile, click the import pull-down tab, and choose Blog/RSS. If you want to import multiple feeds, you'll need to combine them into a single feed. For this, I use RSS Mix. You can see my example RSS Mix feed here. This will import your Instructables activity as "Notes" on Facebook.
You can also link your Twitter account -- with Instructables activity through Twitterfeed -- to Facebook for status updates. On Facebook, I have all my Instructables activity syndicated both through Twitter and through Blog/RSS Notes. I find that some people just follows status updates, while others want the additional information available in the full-text of a note.