If you've ever wondered just how much time it would take you to play through your back catalogue of Steam games, then SteamLeft will have some interesting information for you. Public profiles can be entered into the site, which will then scan your account and tell you how long it would take to beat every game in your library (you can either enter a publicly viewable profile or sign-in to Steam via the site's homepage - we're not sure we can recommend the latter).
The site offers a couple of interesting stats. The longest library checked so far would take more than 42k hours to beat, while the average Steam library would take about 2k hours to beat (at the time of writing it's 2,077 hours). The site also tells you what else you might do with your time, in the example below 783 continuos hours spent game could also be invested in 274 viewings of the film, Avatar.
Thanks, VG247.