What kind of passport do you hold? On the off chance that you're from a country that doesn't qualify for visa free transit, you're going to have a hard time even if you don't leave the airport (btw, tmk it's impossible to connect from T2 to T3 without setting foot on true Chinese soil). In any event, you should definitely leave the airport (and venture further in than the Lido; Friday nights in BJ can be quite interesting).