Of course that upgrading you'll have some new stuff and some bugs fixed...
I don't now any cons of upgrading the phone...
I will upgrade my T610 on a shop that I found here in my city which does the upgrading with the Twister Box...
I already download the RC60005 US2 (latest firmware with my language support), the modem flash and the original GDFS files (to remove the pre-defined items of my operator!)
And,
Merry xmas
=]