Twitch users now have the option to link their Steam account to the streaming service. For Dota 2 players in particular, this should be a nice little feature: you'll be eligible for tournament item drops while viewing streams on Twitch so long as you own a ticket for that specific tournament. Head to the Connections page of your Twitch account to set this up.
"We realize that people have different reasons why they prefer to watch in game or via streams and wanted to bridge the gap of features they were missing out on by choosing the service that works for them the most," writes Valve. "We hope to expand on the features available via this system and would love to hear what you think we should work on next."
This is hopefully the beginning of a larger collaboration between Twitch and Valve. Further incorporating the service into Steam would be a huge deal and, the way Twitch has been making moves in the last year or so, I can see that happening.
Link Twitch to your Steam Account [Twitch]