Hi General,
I just purchased the eTrex 30, it is just like the 30x but with a few less newer options.
Both the 30 and 30x support geocaching.
Depending on what computer you have and the OS installed on it, you might have a few minor problems connecting your computer to your GOS device and have them talk back and forth.
I had zero problems connecting it to my wifes Apple, the auto run feature with the installed software on the GPS auto installed all the programs needed to easily download geocaches to my device.
My other PC has Windows Vista. I had to update the firmware, but all the instructions were on Garmins website.
Just plug in the USB cable and attach it to your device. Visit www.geocaching.com and log in like you normally have, search for caches, once there find the small link "Send To My GPS" once you click it, it will send the whole cache description, hints and logs to your device.
Good luck and have fun.