Reliability will depend on how well the bike was taken care of. The engine is pretty much bulletproof, but its not foolproof (as in, if the previous owner was a fool, who knows what condition it is in?). Personally, I wouldn't recommend the bike for a new rider. Not only is it too powerful (yes, even a 89 600cc bike is too powerful for a newbie, even though its not a supersport), but its HEAVY. Plus, its an old bike, which is generally more expensive to maintain. I had a 2000 Katana 600 as my 3rd bike and would NOT have wanted to start on it due to the power and weight issues. I know it seems like a good deal, but trust me, get a smaller bike to learn on. When you're ready to move up there will be other deals out there.
I concur that a supersport is a poor choice for a first bike. They are not noob friendly. Unless you are just an absolutely HUGE individual (in which case even a supersport isn't for you), a 500 or 650 will give you all the power you could want and then some (500 and 650 are 2 cylinder versus the 4 cylinder config of the 600, so the power and torque are quite different). Incidentally what is your height and build and what do you plan on using the bike for?
This can help us narrow down what would be a good choice for you.