Well, it was originally scheduled for July 2010, but Metro has finally announced via facebook that online topups will be available from Monday 18th.
Better late than never, it will also give a list of previous transactions.
I’m particularly pleased about this, I never use cash any more, and it will be great to have some of the fumbling around topping up metrocards cut down by this (not that its an arduous task). Note though that top-ups are not instant – the site says they can take up to 12 hours to be applied, which is inconvenient.
In addition, you can also update the address and phone number linked to the card – though not the name or the date of birth which, curiously, is listed as 28/04/2010 on my account. (It may be an artifact from when the system was set up?)