Plurk is yet another site attempting to compete with Twitter. Although it has some interesting features, like the timeline view and the ability to share pictures & videos, it still seems lacking. Plurk doesn’t support SMS or IM, and the lack of an API means there’s no desktop client.
Twitter’s main problem is scalability and not being able to handle the user load. There’s no indication that Plurk or other systems can handle that load either. I’m more confident in Twitter’s ability to redesign, re-architect and scale their service, since they have the funding and bandwidth to support their growth.