One of the biggest online communities for Bitcoin enthusiasts is the r/bitcoin sub-reddit on reddit.com. I noticed in the spring that it was starting to gain readership at an increasing rate, so I decided to track the numbers. Here's the result so far:
Unfortunately I didn't get any data points for the last month or so (except the most recent one), but the trend is still obvious. At this rate, readership will double by the end of 2012, demonstrating that there is indeed increasing interest in Bitcoin.