Swimming is good
The last tip by cardsnumber7 in the video above paid off big time for me in a recent game of Bad Company 2. On Arica Harbour, the 3rd base, swim as far as you can and you’ll surprise a few people.
I shot a sniper who was climbing a ladder, but got killed shortly afterwards. The second time some of my team followed me but they got out at the previous ladder.
A medic was standing right over the ladder watching the water but didn’t see me. When he left his position I snuck up and put a few rounds in him! I took out several other snipers too, discouraging them from using a high crane as a vantage point. Unfortunately my broadband disconnected but thankfully my stats were saved.