I always did this, and also turned off the gas supply to the furnace, back when I had a standing-pilot furnace (and back when we used to have "summers" in the Seattle area -- we were running the furnace in August last year and it's humming away right now as we speak).

I never had any problem getting it to light again except that it usually took a few minutes of holding the "pilot" button down until the fuel/air mixture was at the right ratio for the pilot to burn. There always seemed to be a lot of excess air in the lines for some reason and natural gas likes a very narrow range of mixture ratios to burn.

If you are capable of changing the thermocouple yourself or know someone that will do it for a reasonable price I would shut the pilot off and gas supply to the furnace also. The reason I say this is I had to replace my thermocouple every other year or so... sometimes each year I fired it back up. They will usually run for years... but after being cold sometimes they just give out.

If your pilot uses a lot of gas like mine did... the cost to replace it was minimal compared to the amount of fuel it would consume through a summer.

There are kits to convert one to electric ignition and I think the prices are getting more affordable but I am not sure how much of a pain they are to install. I am sure someone in here knows about them and if they are worthwhile.

I would like to know about these conversion kits, if I put in solar HW (I only just replaced my B-vent type HW heater last year and it's a 9-year warranty) I was wondering how I'd get around the fact it would be running a pilot light, and would be wanting to heat the water immediately after use, rather than letting the solar heat it.

It is my suggestion to leave the pilot light on. The pilot light helps to keep things dry in and around the burner area. I'm not saying this is energy efficient, I am saying it will be cost effective for you. I can say from much experience, energy efficiency for the end user is not always cost effective.

What I have seen through the years and thousands of units, is turning off the pilot light causes more problems than it solves. It saves you a few pennies a day in gas but after you have one repair call to have a thermocouple replaced, and orifices cleaned, rusted/corroded parts etc., it will cost much more than what you would have ever paid for the gas to keep the pilot lit.

Keep it on as long as possible if u have a direct vent space heater, cause the pilot fixture at the flame will corrode quick when off from wind and outside air. Keep it on late summer till mid spring in Vermont