Interesting. We don't have a procedure on our 777s for increased Vr for suspected windshear (we have the Improved Climb mentioned earlier) but we do go full length, full power and F15. Or not go at all, which is the preferred option!
IMHO, problems are caused by no differentiation between wind shear and wind gradient and the ambiguity present in most manuals about procedure.
I've come into LHR on a nice day with 15-20kts down the runway with "Windshear reported, loss of 5kts at 200 feet" on the ATIS. No !!!!! Sherlock! What were we expecting here? All around, people with shiny new stripes are briefing for W/S G/A, lining up with full power on the brakes, etc.
You also get "Windshear advisories in effect" at US airports, which I take to mean the system is working, not that there are actual windshear conditions present. I haven't been able to find a reference - does anyone know whether this is a correct interpretation?