I've had my 1st gen TC since its been released and its been running flawlessly for many years. I've read many horror stories online about the TCs breaking down but fortunately I've had no issues. at this time the 1tb hd isn't enough for my backup needs so I'm installing a 2tb western digital caviar green hard drive.
I'm also doing a fan mod by cutting a hole in the metal tray to allow better airflow. overall the install was pretty easy and took about half a day. i must warn you guys its not the prettiest job and i would do somethings differently if i had to do it again.
heat up the rubber with a blowdryer and peal it off slowly

remove the 10 screws
bottom tray removed
old 1tb hard drive
new 2tb western digital caviar green hard drive
remove the screws from the old hard drive and install them on the new hard drive
remove the fan by pushing out the rubber tabs. (its a lot harder to install the tabs back into the plate.i used a tiny bit of dish soup on each tab to help them slide in easier)
fan removed
cut a hole in the rubber backing and metal tray
i added a fine metal mesh so protect the fan from debris
i also made 10 holes in the rubber where the screw holes are. doing this will allow me to open up the TC without pealing the rubber backing off.