A quick update from ESOC, ESA's mission control centre for Gaia:
Winds (high-altitude), weather and solar activity are all green for launch
ESA's Estrack ground station network reports all stations involved GO for launch
Stations at Perth, New Norcia (in Australia), Cebreros and Masplalomas (both in Spain) are all configured; The 15m Perth antenna is in acquisition mode - it is set to pick up first signals from the Fregat upper stage around 39 mins after liftoff.
All ground systems in the operations 'ground segment' are on and ready for launch
Ground Operations Manager Bret Durrett (the guy at left, below) says: Everything is very smooth!