As the popularity of twitter grows so does the reality of the celebrity impostors. I find this only amusing because I saw this happening with website. I am amazed at how many celebrities don't own there own name as a url. It's like the whole publicity, agent circle was completely asleep when they built the internet.
I mean come on $10 bucks to secure your name as a URL. Hello! $5,000 a month for my publicist back in the day so that they could ignore the web.
Case in point: I remember asking my agent if she wanted me to build her a website and she basically said, "No" because she didnt see a benefit. Comically a few years later she actually said to me, "Hey have you seen the website, I'm so excited." Really you can't make this stuff up.
Finally I am reminded of my buddy Dat Phan because part of his impetus to start building his myspace profile was that someone was pretending to be him on myspace. This guy was thanking people for congratulating him on winning last comic standing.
FINAL TIPS: Get the url with your name even if it's the .name. especially if you are branding yourself. Get the twitter.com/yourname if you can as well again branding yourself before someone else grabs it. If you have common name then try adding the activity or category that people will most likely search for you under. Also you always add the word BLOG behind your name and start a simple blog site.