If you are taking about "Full HD" its 1920 x 1080 pixels which is the equivalent of a 2MP capture. It will be shot at whatever shutter speed the camera was using at the time which can be 1/30th sec. so if movement is in the frame it may be blurred.
Heres a frame from a GH1 video at almost full size so you can see what its like. (resized slightly downward to take account of the sites limits)
At 300 dpi this would give you an image of 16.26 cm x 9.14 cm or 6.4 x 3.6 inches. so it would print decently at that size.
Good enough for web resolution obviously and small size printing.
It's easy to do and the quality isn't bad at all. I use a product called Movavi, as it allows me to convert to any format and level of compression, rotate video and do exact capture of single frames. I did have an example of a still that I captured, but can't find it just now.