What Stansdead said.
The company apparently decided that its rate of expansion 2002-2006 was inappropriate as the economic storm clouds started gathering. Profit was well down from expectations (though much of that can be laid at Virgin Nigeria's door), and costs had not been contained as well as they might have been. Early this year, it was becoming clear that there were more difficult times ahead for the industry - especially at Heathrow - and that Virgin might do better to concentrate on extracting the most from its current network, rather than stretching resources on expensive expansion.
So, the current recruiting hiatus. How long will it last? Who knows! Virgin hasn't ever stood still for long, and I doubt it will this time. Officially, there will be no further expansion until the 787 arrives. Unofficially, if opportunities arise that can't be ignored, they probably won't be!
If you've read Flight this week, you'll be aware that Virgin isn't the only organisation that thinks a downturn in airline growth is imminent...