Go for it! I started commuting in downtown Boston during rush hour, right down Massachusetts Avenue... after not riding a bike for about 7 years. You learn pretty fast what works and what doesn't. Find a system that gets you out the door fast, rather than spending an hour getting dressed. You may do well to look for a well-built used bike that looks pretty crappy, so thieves may not find it as enticing (and also get a lock). If you're turning left, take the left turning lane. Don't run over people, etc...