There have been murmurs that this feature exists, and now it's officially in Beta: Steam now has a trading card system, which combine with a Profile Level and more badges.
You can only get half of a set of cards per game you play, so you will have to browse the community areas or ask friends if you want to complete sets...
Cards are awarded depending on the game you are playing, and are not tied to achievements, just playtime. When you end up completing a set of cards, you'll get a game badge, along with a random emoticon (=D), a random profile background, and a chance to get a coupon for another steam game. You'll also get 100 XP, to help level up your profile.
The Steam Level, according to the FAQ, is: "a quick way for users to see how much someone has invested in their Steam account, and how valuable that user is to the rest of the Steam Community". However, the steam level will also be tied to the maximum number of friends you can have on your Friends list, which could be quite restrictive.
This all comes with a bit of an overhaul to steam profiles, which will let you show off showcases of achievements or other account related stats, along with the new game related backgrounds you can get.
In the classic format, this is currently an invite-only beta; except of course when you join, you'll get some keys to give out to friends. And then more keys. Until your steam inventory is nothing but DOTA 2 and Steam trading card keys, forever more.
Do you guys think this will help make the community more active? Do you actually visit your friends profiles at all? Tell us below!