is that it's easier to transmit AC long distances. The reason is that the amount of energy lost in transmission is related to the current (amperage) you send through the power lines. To get a given amount of power (megawatts) through a given line, the current is inversely proportional to the voltage. Restating Ohm's law:

Voltage = current * resistance
Power = current^2 * resistance
Power = current * voltage
Power = voltage^2 / resistance

Here's an Ohm's Law calculator to play with.

High voltage transmission means you need fewer amps to carry a given amount of power through a line, resulting in lower transmission losses. The problem with long distance DC transmission is that it's more difficult to reduce the voltage at the consuming end than with AC. To reduce AC voltage, all you need is a simple transformer. However, transformers can't directly work with DC. You'd need some form of inverter or chopper circuit for the DC in order to use a transformer.

The interesting thing about solar power is that you may not need to worry about long distance transmission. You might be able to produce the electricity closer to the point of use. As for DC use, it could work for most things we have in the average home or business such as cooking, powering electronics (most electronics systems have power supplies to convert the AC to DC anyway), etc. You'd need to change most of the electric motors in things like air conditioners and the like because the AC motors won't work with DC.