For almost all the interviews I have done upto now, I have made it a habit to do a search and evaluate the online presence of the candidate in question. I now come to believe that it does play a big part in influencing my mind and at times had gone to the extent of creating a level of respect towards the interviewee.
The frankness exhibited, the technical skill shown and the ability to articulate in blogs, forums and social networks allows to project a great personality. Before a professional interview getting this mind share of the interviewer even before walking in and meeting face to face is a huge bonus.
Personally I have had different experiences with my own online presence. Once I got into a call with a customer and he greeted me by saying - "Hi, the fan of rubber slipper" - I was stunned, wondering why me and how? Thank god it was a call, I recollected my conciousness and replied. Yes that's my favourite and asked how do you know? He asked me to google and see. Soon after the call I did a search to find that facebook was the culprit. But then I was glad that I have been either lucky or he was very kind to avoid talking about the embarrassing topics that my "friends" have put up about me. But it was indeed a lesson on how important online presence is even if you are not looking for a job.
Second time it helped me when the customer got to know that I know a bit of MySQL and treated me as a techie and not as a complete business guy who comes to bluff!
I guess in the modern era a good online presence is important as much or even more than the CV. Do a small test to google your own name and see, what's getting listed. If you don't have a linkedin go create it and keep it properly updated, if you are into facebook go and set your privacy policies to control who can see what. This would atleast set the basics right.
Also remember if you are single imagine your proposed/about to propose/crush guy or gal doing a search and finding that you are a crap. God bless you :P. So atleast for this get started and get your online presence in order.lol
PS: my online presence is any way hopeless due to the type of friends I have so I have given up on it.