I've done it. Without a doubt there is a high barrier to entry, but with anything you have to start small. Find articles that aren't fleshed out already. Find things that are entirely incomplete. Dive into those articles first, those are the ones that need attention, not Barack Obama's page. I started getting involved with wikipedia about a year ago. If you start small and create a history of trust, older users are more likely to trust and approve your edits.