I read somewhere that USB and eSata have limits to how many "pairing" is can have. does this mean if it's ejected and re-inserted into the slot more than 1500 times it will just stop working? or does that mean x number of devices?
What that means is the materials the cable and the socket the cable connects do can be inserted and removed 1500 times on average before something "bad" happens that makes it stop working.
What is "bad" could be anything, it could be the plastic cracks, it could be the metal contacts wear out, it could be the solder inside the cable breaks free from its contacts, anything! The important thing is ON AVERAGE (it's not like there is some counter inside where it works on the 1499th time but it shuts it off on the 1500th time) you should be able to plug and unplug the cable 1500 times before one of those things happen.
Also note that the specifications are minimum numbers. If someone wants to make a device that can handle 10000 pairings that is fine, it is just they can not make a device that handles under 1500 parings and still legally be allowed to use the USB logo () on their products..