If I'm interviewing someone, I will go research them beforehand. I've been handed resumes, and gone and done a google search. If there's no blog, no sourceforge/github, no homepage, no mailing list chatter, I've had that weigh in my decision.
Previous work is listed on the resume.
I didn't suggest stalking a twitter feed, but googling for me would indicate I do have a twitter account. And a blog. And a github account. And a podcast. And that I run a local user group.
To then be asked "so, what's your involvement with the tech community?". Or "what sort of tech work do you engage in outside of office hours?". That's just lazy. There are 2 people on the planet with my name. This isn't a case of "John Smith"-itis.
I also hate the calls from recruiters (I don't often take) that start with "I found your resume...." and end with "... send me your resume". Umm... you have it. YOU FOUND IT ONLINE. THAT'S IT. Sure.... they may have found one from 8 years ago - I get it. I tell them - "it's updated on my website and in multiple formats". If they can't be bothered to go to my website to download it, we're off to a bad start and this relationship isn't going to work.