Can you help me with these water heater problems?

Two different water heaters, two different issues:

1) My step-son’s electric water heater has been cutting off periodically for the last several weeks. Like it’s tripping some kind of switch (though not the breaker for the water heater). He pushes the red “reset” button, and it comes back on, only to repeat the cycle some time later. If it matters, it’s a relatively new townhouse, maybe 8 years old. What could be causing this?

2) My gas water heater is acting up, as well. My water doesn’t seem to be as hot as it used to be. I have to turn the hot faucet on all the way, and the cold one no more than half way, in order to get a hot enough shower. It runs out quicker, too. By the end of my short-ish shower, I’m rinsing in cold water. NOT FUN. This water heater is probably just getting old, but is there anything I can try before giving up and buying a new one?

Bonus question: If you had to buy a new water heater, would you spring for one of those tank-less ‘instant’ water heaters that are out now? Pros and cons?