I don't think you need to worry too much about this Gavin. People who post images to a forum already know they are going to be seen by lots of people. I have checked an upload I made to the forum from my mobile phone and checked it in Adobe Photoshop (where you can see alot of info about a photo, and also you can add a lot of info as well - this is part of the embedded metadata) and there is no information given about the image apart from the actual time I screen grabbed it. I am going to upload another image in a minute from my digital camera to see how much information that retains and will let you know ( so please ignore a non relevant post to this thread). It maybe that the forum software strips all the infomation out so as to keep the image size tiny and not overload the system. The guy on the vbulletin forum who is complaining about headlines/descriptions being stripped out has used the Adobe software to put this information with the image and when its uploaded its no longer there. I don't think our guys will be adding lengthy descriptions, etc, more like a headline below the image and a few pithy remarks.
As Neils says its possible to add a location via GPS and I can add default locations, times and dates on my digital camera, but never see the point of it really. Might be useful for a professional news photographer though.
I know some of this because I have a small photo library and still sell images through an online portal so adding information and keywording is something I'm often, and hate, doing.