Recovery Mode
The stock recovery mode on the TF101 shows one of two screens; a green android in the middle of the screen with gears turning inside it, or the same android with a yellow triangle with an (!) inside it instead. The gears obviously mean it is working (flashing firmware), the (!) means something has gone wrong (no file found, flash failed). To enter recovery mode, you need to press and HOLD Volume DOWN and POWER when the device is powered OFF. As soon as the screen comes on, RELEASE THE POWER BUT HOLD THE VOLUME STILL. You will see white letters appear in the upper left corner of the screen, it is now okay to release the Volume DOWN button and quickly (within 5 seconds) press the Volume UP button to enter recovery mode. There are also applications, such as Reboot to Recovery, available on the market, that will allow you to reboot your device with one click into recovery mode without having to toggle your power/volume buttons.
About Stock Recovery Mode
The stock recovery mode is absolutely required to install official Asus OTA (Over The Air) updates. Unless your device is unrooted with a stock recovery mode, you will not be able to install any OTA updates, this includes ICS!! It can also be used to install (or RE-install if it were) your STOCK ROM (only official, digitally signed files will be accepted by the stock recovery to flash over the firmware, no modded roms will work). The method for doing this is outlined in the link for rolling back your firmware version above but I will summarize;
Recovery mode searches your external SD card ROOT DIRECTORY(and the internal memory's cache directory, but this is not useful for any practical reason for you) for these Asus files. The files must be named either;
EP101_SDUPDATE.zip
or
XX_user-epad-Z.Z.Z.ZZ.zip (X = firmware region stamp, WW, US, DE, etc, and Z - firmware version, 8.6.5.19, 8.6.6.21 etc)
I personally find the second configuration to work best. If stock recovery finds a file named appropriately and signed with the proper digital signature it will install it, and you will see gears turning. Otherwise; (!). Remember, it has to be on the SD card in the ROOT, not in a folder or it won't find it.