Did you do an FDR (factory data reset) after you installed ICS? If not, you need to do this. Many people, myself included, saw issues after doing the OTA that the FDR completely cleared up. The phone should be even more responsive and overall quicker.
When you do the FDR, save all your data for any apps, such as data for banking apps, to the SD card and pull the SD card out before the FDR. This is esepcially important if you have a lot of multimedia files as there does seem to be an issue where after the install or an FDR ICS tries to index media files and this can take several hours and slow the phone down a bit. After the FDR, just reinstall your apps from the Play Store, import any data back into them from the SD card and you should be good to go.