On the "Friends" tab.
When someone in your friends list is playing other games. Instead of putting "playing other game" under its name, you can just simply put the title of the game he/she is playing.
This will help new Steam users via Dota 2(which is a lot) to notice those games.
Since Dota 2 will be Free to play and it will pull tons of new users on steam and will spend most of their time in dota 2 interface than steam itself, this is a simple yet better way to promote other games without bashing it to their face.
And if those games pick their curiosity enough to check what the hell his/her friend spending his/her game time with, you can put another option together with "View Dota Profile", "View Steam Profile", "Send Message" etc. with "View Game Currently Playing". This option will open a browser like viewing their steam profile but will show the game's steam page.

I hope this suggestion helps,
feel free to post your reaction or feedback below. Specialy Dota 2 players