You can bank your entire years worth of points if you want. This has to be done within the first 8 months of the UY.
It can be as a one time transaction, or over multiple ones (ie: bank 20 points this month, 20 next, etc.).
Once banked, those points would only be good for the following UY. So, if you bank all your 2010 points into your 2011 UY, those points now take on the travel dates of the 2011 UY points an will expire at the end of that UY.