Last night I met a local triathlete who does some coaching in the area and has been a swimmer forever. This was highly appealing to me because he's done both swim-swimming and triathlon-swimming and understands they are different. I swam a few laps while he filmed me above and below the water. The underwater shots were done using a nifty reverse-periscope attachment for his video camera (camera stays out of the water, periscope goes under).
Having never seen myself swim, it was an eye opening experience. I also got confirmation that I should continue to wear a hat to avoid massive sunburn atop my head

I've been swimming about 2:00/100yds and can do a continuous 400 yds, but get winded, tired and my form degrades over the distance. (I don't often do a 400 yd set.) 21-25 strokes per length is common for me. With the desire to do a HIM in September, this was not good.
After a few corrections, the biggest being extending my stroke, reducing my stroke rate, and breathing every stroke (well, every right) I immediately dropped to 17 strokes per length at the same pace. Those changes also fixed some other odd mechanics I had like a wicked cross over when I breathe, and a crazy wide scissor kick trying to compensate for the cross over.
I still lift my head too much to breathe, and I still, out of habit, try to counteract by dipping my extended left arm down, effectively ruining the pull for half my swim, but now that I know that I'm doing it I can practice fixing it. (He recommended some drills to help this out.)
It was really a great experience and I'm so glad I did it. I'll be hitting the pool today at lunch to burn it in