When doing a route search (only) on the flight status page
Virgin Australia Flight Status it appears with a wifi symbol next to the flight number. This only appears on aircraft that are actually internet connected (wifi entertainment doesn't count as the entire 737 fleet has got this).
At this stage the fleet wifi connection is:
B737-700 = 0/2 - 0%
B737-800 = 67/78 - 85.9% (based on the flight status page)
B777-300 = 5/5 - 100%
A330-200 = 2/6 - 33% (based on the posts above)
The 737-8 connections appear to have basically stopped as April this year saw 84% of the 737-8 fleet connected and I've got my doubt's about the rest actually being getting it because the remaining 11 are the oldest in the fleet.
For comparison Qantas has around 66% of the 737's connected and half of the A330's.