Yes, definitely – we're working on how to make it easier and more attractive to add instructions, so hopefully you'll find more of them in the near future.
Tumblr integration is high on the list. Since we're working with very limited resources right now, it might take a little while till it's released, though.
As of now, you're not missing anything. We started out as a place to collect stuff we made Pinterest-like, then discovered people wanted more Instructables-like information, and are now working on the – as we think – missing links: Connecting ideas via "remake/remix/inspired by" links and changing from a push-model of knowledge sharing to a pull-model.
As we are bootstrapping right now, things are moving slowly, but we hope in the right direction...
The idea behind todayimade is to collect and aggregate ideas for DIY projects in a very broad sense – stuff you make, sew, cook, craft, build etc., and to let people build on each other's ideas. Right now the feature set is really small, but we hope to implement stuff like "tell me more about how you made this or that" and "this inspired me to do that" in the near future.
Thanks all for your feedback! In fact, we're aiming at being "Pinterest meets Instructables" – knowledge porn for makers. We're in our very early stages, so the HN induced traffic surge hit us a little unaware. Also, we are working steadily on our posting and sharing features to get more instructs on the site – any feedback on that is highly appreciated!