Make sure that you haven't undervolted your CPU too low. I exeperienced reboots/freezes then went to voltage settings and added 25mV to each frequency. Problem then went away.
I use GO SMS PRO for short messages. On 2.5.4 I cannot make it to receive the messages as primary app. Whatever I choose the stock SMS always gets the message and display notification. Everything was perfectly fine with previous versions.
Aternatively you can block Market from updating to reduce 3G data. Download terminal emulator from market, fire it up and execute the following commands:
$ su
# touch /data/app/com.android.vending-1.apk
# busybox chattr +i /data/app/com.android.vending-1.apk