I'm pretty new to BA as well, but already I've heard of 3 guys who have been with the company for less than a year leaving, at least one to Virgin. All have put in their resignations since Christmas.
Reasons given are the same; 750hrs/yr vs 900 ; broadly comparable pay despite that for a new joiner ; a pension which is almost 30% better! (surely there isn't THAT big a difference?) ; a decent chance of command within a reasonable timescale.
Must have been a shock to BA's management who still seem to think that theirs is the only airline of choice for anyone after a job. Virgin does seem to be a happy company to work for though. Pity I wasn't good enough to get there