It's a great bike. the suspension is a lower grade but the 98 is a great option for someone who likes the older style SS yet wants the newer motor with the 3 phase charging system. They are fairly bullet proof. Make sure the cam belts are not old (past 2 years or 12,000 miles)
The bike is due for a major service at 6K miles. It's a friend but I'd calculate the cost of the service into the deal. BCM in NH is prolly the best place to get it done near you. Plus, they aren't that expensive.
How much do you weigh? If you're over about 170 lbs, the stock suspension may need to be reworked - if it can be at all. The problem with the SS/CR's is that they had crappy suspension (some of the suspension being unable to be worked on - except for fork oil and springs).
A lot of the issues on the carbed 900ss bikes were fixed by 1998 so there are less worries with that model year. Plus, like the NCRick said, you have some nice updates - especially the 520W alternator which allows you to run some electrics and farkles should you desire.
Here's a list of the various changes in the models years for the carbed SS bikes. They are great fun and if properly maintained a workhorse!
I ride my wifes 98 900 CR and after putting new springs and some 20 w oil in the forks it actually rides well. I like it just fine if I am riding in a normal manner. If I try to ride it very hard and while on bumpy roads, it really shows the weaknesses compared to my 1999 SS that has the Penske converted Showas in the front and a custom valved Penske on the rear along with light aftermarket wheels.
After my wife has more time on the 98 I will likely stick a set of redone Superbike forks and a Penske shock on it too.
It kind of depends on what you want from it. The stock CR is still better suspended than a Suzuki SV as an example. Just plan on the springs and oil for the forks. The stock fork springs are way soft.
check the top frame tubes where they are welded to the steering stem, they are known to crack there, here in oz, they replace the frame under warranty still, but the owner pays the labour portion. other than that, how the chain is lubed and how clean the motor has been kept is a good indication of how it's been mechanically looked after. and as NCRick says, check the cambelts or get the 6k service done and use that to haggle.
The SS is a great bike and normally at a fraction of what other dukes cost. A few upgrades are needed the seat is a piece of crap (trying to source one in Australia at the momment), rear suspension could be better, bars are hard on the wrists on long trips (set of heli's in the future). But there is nothing like owning a Duke. Guaranteed people will walk straight past the latest greatest jap rocket to look at any Duke. Brakes well, turns OK. Get the latest you can afford. Toying with the idea of injecting mine.
Forgot, the viatalloni mirrors really suck, get a set of decent ones from Cyccon.
Classic, old-school Italian crotch rocket looks, more than enough power for the street, when you start to hit the wall on the handling limitations lots of alternatives are available. A combination of sound/looks/style/mojo that only the most hyperexotic Japanese can exceed. CRs rock.
I was just thinking about a group of us out on Sunday.. My 01 SS, 2 Hyabusas (Hyabusii ?), new VTR, new VFR, 1700 Road Warrior. We pulled up ouside a pub for lunch walked up the stairs and 2 blokes said "Nice Ducati".. we walked in as a group... What can you do but smile and say thanks..