I love snorkeling. Especially because not too far away there are nice sites with lots of colorful coral and large numbers of tropical fish.
The reason for a submersible would be to open up this world to my children and other family members and friends that are not really capable of snorkeling.

I found these plans. and something really amazing here.

Anyone here ever did this, or am i really mad to want to do this?

I have seen the one man sub before it was in Mechanics Illustrated back in the early 80's. I think it would be fun. The dolphin boat thing is something els I watched the little video and it looks pretty fun. Not much for under water though.