Been a long while since I upgraded MS office so the jump from 2003 to 2010 has come as a supprise.

2003 65535rows x 256columns
2010 1048576rows x 16384columns

A big step up.

Only thing I noticed is if Office 2010 is in "Compatability Mode" meaning it's running to support the older xls format then you will be restricted back to the 2003 limits.