I think most venues have more or less abandoned trying to stop fans taking pictures - the advent of mobiles and the net has seen such a proliforation that its an unstoppable tide.
As a general rule, if you are obviously a fan taking pics for your own use, they won't be too fussed. If you were using a two-grand camera and snapping from the front row, that would be an issue because professional snappers usually have agreements about where their work will be used, and they can be relied on to get god quality shots that will show the artist in a good light (literally!)
So as long as you don't make a big deal about it, be discreet and keep your eyes open for security, you should be OK.