A plasma anti-glare filter is worth it if you have a window in the same room as your television. It will reduce the reflection of the light on your screen. If you are watching your TV in a dark room, you do not need it.
The following pictures compare a plasma with an anti-glare filter, one without, and an LED television. As you can see, a normal plasma is almost as reflective as a mirror. The filter does a good job at both diffusing the light and reducing it.
A plasma anti-reflection filter is a thin film applied on top of a plasma screen to reduce the reflection of the ambient light. Compared to an LCD, which can have either a glossy or matte finish, plasma absolutely needs a glass panel to contain each gas cell. Glass is a very good reflector of light, so if your room contains a window, you will most likely see the reflection of it on your television.
A plasma anti-reflective filter is definitely worth it unless you do not have any windows or lights where or when you are watching television. It does offer a considerable reduction in the amount of reflection on the television.
That said, an anti-glare filter for a plasma television will reduce the brightness of the picture at a vertical viewing angle. To further reduce the reflection, manufacturers assume you will only watch your television at relatively the same height as the TV itself. This assumption is useful for them because they can block more of the light coming in and out of the television at a vertical angle, like most reflections of lights and windows would. Therefore, if you are watching your television at a big vertical angle (like if it is hung on top of the fireplace and you are on the ground with your kids), a plasma anti-glare filter might actually be worse for you.
If you already own a plasma TV with a lot of glare and reflections, you can still fix it by buying a third party anti-glare filter and applying it to your television. For example, ViewGuard makes filters that goes up to 65" in size. It is not cheap, though, depending on the size of your television.
Of course, the best solution is to adapt your room accordingly. Installing curtains on your windows or moving your television to a better spot is an effective method of reducing glare and reflections on your television.
The Panasonic Infinite Black Panel with Louver Filter is the anti-glare filter of the top of the line Panasonic plasmas. It is available on the 2013 models ST60, VT60 and ZT60.
Samsung Real Black Panel is Samsung's anti-reflective filter as described above. There is only one 2013 model that includes it, the F8500.
LG's TruBlack Filter is LG's term for the anti-glare filter that comes with its higher end plasma models. There is no 2013 model that includes it.
Unless you have a complete dark room when you are watching television, an anti-glare filter for a plasma television is worth the upgrade. It does not remove all reflections, but it offers a noticeable improvement.