BA has launched a 30% bonus for buying Avios running to 2nd August. The maximum 31,000 Avios will cost you £399. This is, however, still more expensive than the current offer for buying BMI miles that I wrote about recently and which runs to 30th June.
According to this FlyerTalk thread, Amex has changed the conversion rate on the International Dollar Card Membership Rewards scheme from 1:1 into Avios to 3:2. This closes one of the most interesting loopholes available, whereby you could get an IDC Amex, transfer your UK Membership Rewards balance across, get a bonus equal to the current UK / US$ exchange rate (so roughly a 60% bonus) and still get the same 1:1 transfer rate. The airlines are now in line with the hotel IDC transfer rates, which were already about 50% weaker than the UK MR transfer rate. Delta, SAS and Flying Blue have also moved to 3:2, whilst Malaysian, Iberia, Cathay, Virgin, Finnair and Singapore remain 1:1. You can of course transfer to Iberia and then to BA Avios (although your IB account must be 90 days old to do this) although it is debatable how long this will last.