Presets should be backed up in a configuration file. Find the file and you should be able to drag it to a flash drive to use in on another computer. But then again you can just save the session and open it on the new computer, the settings will be saved as well.
I usually start with a blank slate on my plugins. But since I work on location recording classical music, sometimes presets are usefull for duplicating multiple sessions using identical setups and instruments. For instance, I recently recorded a pianist on four different dates, in the same room, with the same miking setup. I created a preset from the first session on the EQ and the reverb and used that for a subsequent sessions to obtain an identical sound. I will say, unless you are working with familiar and predictable source material, preset are never reliable without tweaking.