I lived on the beach, waterfront, actually pretty much in the dune line because my house was old enough that the dune line shifted after the home was built and was grandfathered in.
Pros -
The view. I adore water, I can stare at it for hours at a time, I loved my super shaded back porch (or front porch - it didn't seem to have a dedicated front/back).
The air. I rarely used A/C because of the constant breeze that would sweep through. Sliding doors on both sides of the house, so I could create a wind-tunnel effect (which was also a con).
The vibe. I love beach communities. I love how relaxed the locals are off season. I love how it feels to constantly be in that state of salt and sandiness. I felt so lucky to live there, always in touch with the outside, always in touch with fresh air and water. It was good for my soul. And my skin! I don't think I've ever been happier living someplace in my life.
The cons:
Insurance, as everyone has said. It's a bear. For me, because I was living someplace very inexpensive, the insurance was practically as much as my mortgage payment.
Bugs. I couldn't keep them out of my house! My place was on "stilts" or whatever you call it. It was elevated off the beach. Palmetto bugs that look like huge roaches (but they can FLY) would march up the pilings every day, so you couldn't hang out "under" the house. I sort of envisioned having an entire shady deck down there, but it was a no-go. Also I couldn't own anything leather as it would mold, but that was a climate issue...
Weather. The constant wind was 90% great, but the 10% of the time that it was bad was almost unbearable. I was always replacing shingles and shutters and sometimes windows. $$$$$$$$
Tourists. It's hard to accept that you have to battle 30 minutes of beach traffic to get to the store 2 miles up the road, all of your favorite restaurants suddenly have 2 hour waits, people are rude on vacation, people would camp out in front of my house on the beach and throw trash around, scream constantly, have sex (twice I saw this, wish I hadn't) or pee under my house.
I should add that 6 years after I moved away, my former house and in fact my entire neighborhood was completely destroyed by a hurricane. The pictures of it afterward were nothing but beach with some sticks coming out where the pilings had been.