I have used plurk for quite sometime now.

About a year ago i started tweeting, I was so in love with twitter that I wanted ti discover alternative to twitter to use when twitter is down. That was when I registered on plurk.

Plurk is easily the best alternative to twitter. Plurk is clourful and vibrant and has the 140 char limit, I especially love the Karma feature or points which increases if you are a regular updater or post quality updates.
Timeline display is innovative and you have an inbuilt integration to post on twitter simultaneously.

While twitter is more about text based updates plurk is lot more than text and plurk is more interactive than twitter.

But plurk is more complicated to understand than twitter and then twitter also has this global appeal and more users with celebs joining it. So twitter rocks any day but plurk is good competition which can give us better of twitter. But still if you want something new like twitter plurk is the answer.

If you want to try plurk register here www.plurk.com