Penny, I have only used 2D seismic, except for my work on the Hosgri fault I was able to use paper records every 1 or 2 km out of a 3D set. A lot of the 2D data are rather good though...all of Western Geophysical's offshore data are now on-line from the USGS. One problem with 2D data is that migrated strike lines do not "tie" migrated dip lines, if the reflections are dipping. Makes it more tricky to keep regional stratigraphic correlations correct.

Not sure what the double reflection from the seafloor is...a bubble pulse? "G.I." (generator injector) airguns are used which keep the air bubble generated by the initial impulse from collapsing and reverberating. These work rather well. These are used in academics and USGS: I assume industry uses them also.

As for the tent...yup, still used...it actually collects a fair amount of oil (and gas?) that is used, so they probably make money off of this. Still a lot of tar on the beach around there, though. The tent only gets one of many seeps.

Others...sorry, this post was pretty full of terminology. Penny will follow this. Maybe she can translate if asked.
Chris