My hot side on my water heater is always hot. Is this normal? If not what could be causing this?

Yep, this is normal to a certain extent. Usually the heat will radiate up a couple feet on the hot and cold lines. However, if you have a recirc pump on the system, the whole hot water line will be hot. Also, a leaky hot faucet in the home, or a faulty mixing valve will cause the hot water line to be constantly hot.

You may have what I like to call, a free recirculation system. IF you have hot water almost instantly
At any of your mixer valves that are down stream from the heater. That's after a non use time of about an hour, your mixer may be bleeding hot to cold and causing a recirculation .the only problem with this is now your cold system is hot and your water heater will run more frequently. Check your hot water pipes that are
Away from the heater after non use. If you have blazing hot pipes all day there is something allowing the hot water to flow IE: as the man said a mixer valve is usually the culprit.

I know little to nothing about plumbing, but got the wikipedia answer on what a mixing valve is. Where would these be located? I appreciate both of your answers, but neither of you have confirmed my fears. This of course is good news.
What are the chances that I have a cracked hot water line under my slab? Would this cause the heater to constantly be piping hot?
Since my hot line on my water heater is constantly hot, is this likely to wear my water heater out fast?

If possible could I get your advice on my latest post to my question?

If possible could I get your advice on my latest post to my question?

Any single handle fuacets contain mixing cartridges. And yes, it is possible that there is a leak under the slab, but I really hope this isn't the case. With all fixtures shut off, go to the water meter and see if it is moving at all. If it is, this indicates a leak in the system. Hoping you the best of luck.

I agree with MGD if your concerned about a leak, turn all faucets and any automatic watering devices off.
Then go to your water meter and see if its moving at all. It should be totally still or show no flow
Whatsoever.If your good up to this point,then by touching the hot lines down stream you will have an idea
What direction the hot water is being drawn because they too will be hot. There is the possibility that
Someone may have installed a thermal bypass valve under a sink or behind a shower to produce instant hot
Water to that device. I don't want to confuse you so I won't get into that right now.the mixers we spoke of
Are valves (usually shower/tub) single handle operators, that combine hot ands cold water by positioning
The handle in various positions,they give desired temp. these valves come in many styles and manufacturers
And each has a cartridge that is connected to the operating handle.any place hot and cold are mixed can be
Suspect in a bleedover so find all your mixers and try to isolate. Keep me posted.

Good call rojo. Turn off all of the water using features in your home, and then take a look at the water meter. A small star or triangle on the top of the meter is the leak indicator, and may be spinning (no matter how fast). Then go back into your home and turn off the water supply to the water heater. Take another look at the meter. If the leak indicator has stopped, then you likely have a leak on the hot water line somewhere.