I have just updated my N900 to 2.2009.51-1.003.
BUT STILL NO USSD FUNCTIONALITY.
Sorry for screaming, had to let it out.
In india those using Airtel GSM cards send message AIRTEL to 121 and reply with your options to view the balance.
Its long way to know but runs none the least.

As for the update is it just my optimism or I think the transiton animation and screen is looking more responsive and alive.
If you get my meaning