One nice thing about Twitter is that you don't need an account or need to be "following" a user in order to view the user's tweets. Here's astronaut Mike Massimino's Twitter page, where you can read what he's tweeting from space. Some samples:
We see 16 sunrises and sunsets in 24 hrs, each one spectacular as the sun lights up the atmosphere in a spectrum of colors.
Just flew over the US, Baja to Miami in about 10 minutes! Beautiful Day!
Getting ready for bed, sleeping in space is cool, tie down your sleeping bag and float inside of it, very relaxing--
...and speaking of Twitter: is anyone (or everyone) you know Tweeting Too Hard?