Are you a cheerful tweeter, or do you incline towards the miserable? A nice little tool called HappyGrumpy can take a look at your (or anyone elses that you fancy) account, and tell you if it's cheerful or not. You have to have a Twitter account in order for this to work, and once you have authorised it, you can start poking around. Here's my data in case you're interested:
Apparently I'm a fairly happy chap, which isn't quite what I was expecting. The tool does a lot more than that however, since it can show you a word cloud of recently hashtags, emotions over a period of time, top positive/negative speakers, daily scores and so on. The tool will also create polls for you and compare brands. It's a fun tool and worth poking around in if you have a spare 5 minutes.