A timely reality check
Dr. Dobb's: Does Twitter pose security-related problems?
McGraw: Twitter presents a perfect vector for malicious code and phishing, especially since most users use bit.ly or tinyurl to fit clickable URLs into their messages. Twitter allows dingbats to cash in their last remaining privacy chit with a coolness factor that often overrides common sense.
In fact, the last point applies equally well to Facebook and MySpace. The big problem is many users of these systems seem to have little understanding that postings, tweets, tequila drinking photos, and everything they post in the Web 2.0 world is public. Before Tweeting whatever occurs to you, think about whether you would want your mom to read it. Also note that the Tweet will be around basically forever! Will your future potential employers search Twitter? Why wouldn't they?