Flickr meet-up: Lookit!
Originally uploaded by carpe icthus.
From the perspective of cold logic, it's probably a bad idea for a professional photographer to spend much time in an interactive photographic community not devoted to commercial or professional development, like Flickr. It's not a skill thing -- there are plenty of amateurs more skilled than all but the best professionals -- it's a money thing. Even though, yes, your work can be discovered and I've gotten a number of great jobs from my Flickr page, simply pounding the pavement is going to be a more lucrative use of your time.
But I think they're helpful in an even more fundamental way. Time and time again, I've heard professional photographers say, "I remember when I used to enjoy photography." Turning your passion into a business ca be tricky, and the latter can all too easily destroy the former. If it does, it's probably time to pack it in. Your work will suffer, your life will suffer, and this isn't a job you can do without energy. Communities like Flickr surround you with millions of people who adore photography, from fellow professionals taking three days to set up a shot to new owners taking photos of their pets. It's both intoxicating and rejeuvenating, and the spread of this excitement is going to mean great things for photography as a field.
More than anything else, my professional goal is to still feel slightly giddy when I pick up a camera 40 years from now.