In our area the building officials have started to enforce on the gas lines drip legs. Now l have a question about it. Does it need to be serviceable or visible ? The reason I am asking is that on a new construction inspection I saw one, which will end up behind the drywall.
Raymond, Of course you should check what your local code say.
For starters the drip leg should be as close as possible to the gas appliance. Your photo does not indicate the proximity of the appliance but I suspect the leg could have been located closer.
There are many factors to account for (such as gas makeup, length of pipe, dia. of pipe, quality of pipe, length of drip leg, etc) but very roughly speaking it could 25 to 45 years for that drip leg to fill up.
When the house changes hands next time, how will the HI know that there is a drip leg? I guess its a good thing you took the pic. 
I would leave that one and install another one just outside of the appliance that is visible and serviceable.
Paul Hinsperger
Hinsperger Inspection Services
Orangeville Ontario
www.hinsperger.com
IFGC 2003
408.3 Location of drips. Drips shall be provided with ready access to permit cleaning or emptying.
Thanks Paul, I looked first in the wrong book for an answer.