How can I keep up to date if I'm a member of Treehouse?

Stay diligent, and never stop learning. There are a bunch of free online blogs do a good job of posting about the next up and coming.

• http://www.smashingmagazine.com/
• http://css-tricks.com/
• http://htmldog.com/
• https://developer.mozilla.org/en-US/

Watch the Treehouse Show for free on iTunes every Tuesday. Nick and Jason spend 10-15 minutes presenting 10-20 new things about web design and development.

I'm sure there are many more resources, but that will give you a start. If you're in it, you should be aware of whats changing. If you're out, this stuff is going to blow right over you.

A lot of people say things like "web design moves so fast" on blogs. However, those blogs have a vested interest in people believing that things change weekly in web design so people will check them weekly. Web design in practice changes more like yearly. If you like reading blogs you can check out the ones Kevin mentioned. If you aren't so into those just tune once or twice a year to check out what ground breaking new stuff has come out in the past year.

Treehouse absolutely does update their videos. Just ask anyone who finished the original CSS course right before it was replaced by the current one, which introduces CSS3. ;)

smashingmagazine is awesome. I've even bought the book they publishedon WP theme development.