I run/built mogade.com, which does the same thing. I blogged about how I switched to Redis for this specific feature (it made it top of HN, weren't you paying a

I run/built mogade.com, which does the same thing. I blogged about how I switched to Redis for this specific feature (it made it top of HN, weren't you paying attention that day!?). Maybe you'll find it useful, simple test went from over 5minutes to 147ms: http://openmymind.net/2011/5/8/Practical-NoSQL-Solving-a-Real-Problem-w-Mongo-Red/ http://openmymind.net/2011/5/8/Practical-NoSQL-Solving-a-Rea...