LinkedIn can very easily take control of professional meetups, but no one has the brains to do it. LinkedIn has group, has events, but both features are terrible, lack good APIs and are not integrated.
I would rather join a technical group on LinkedIn with events instead of using Meetup. The community is already there and almost all of us have LinkedIn accounts.
LinkedIn: please fix groups, please fix events.
EDIT: Forgot about Google Plus and events. Another potential alternative to Meetup.