I haven't yet come across a wifi I would consider any way fast, however the ones I have used are good enough for most emailing and social media.
This can be a real blessing....arriving after a long haul flight and you don't have a mailbox of dozens of .messages to trawl through. The prices vary dramatically too.
Let's face it though, BA are behind the curve on this, and with normal BA roll out speeds (as seen by bedding, CW food etc) it ain't going to happen any time soon.
It could make for an interesting thread though - tracking roll out of food, bedding, wifi - anyone who gets all three can shout 'house'. If you travel from LGW on the other hand I predict that you can safely log out until at least 2020. Those 777s are going for densification, an ideal time to install wifi at the same time.