I bought mine new in November 1998.
It's still pretty much standard aside from accessories like heated grips and a front fender extender, the headlight mod, EBC front discs, Goodridge hoses, stainless downpipes/cheapo silencer from Sandy Bikespares and a Scottoiler… though I hope to get round to upgrading the suspension soon.
Like Paul above, it's still on the original battery. I think regular use is what keeps them healthy. (Paul, I changed my fuel filter for the first time earlier this year: the plastic body had developed cracks and was beginning to seep petrol. I opened it up and found the filter itself was quite clean.)
Once the engine got over 90,000 miles it started getting clattery and while a cam chain change would doubtless have helped, it sounded like the pistons were developing a bit of slap too and second gear was a bit iffy as well. After about a year of this I decided a replacement engine was the simplest cure since I didn't want to be off the road for long and fixing up the old one could have become a slow and expensive job.
I turfed out the old motor which now had 115,000 on it (checked the valve clearances again and they were still in spec, never having needed reshimming), bunged in one that I picked up locally for £50 and used that for a year before having to admit that I'd bought a pup. While it sounded as smooth as a sewing machine, second gear was every bit as dodgy as my old motor and it rapidly got worse until it wasn't only impossible to engage, but a fight to get past it to 3rd.
So I bought another engine, this time from a breaker who had had it running and assured me it had no problems. He was good as his word, and the bike clocked up its 157,000th mile just yesterday.
Aside from the usual servicing and consumables it's not needed much else done to it.
Throttle response gets poor because of wear on the carburettor sliders after about 70,000 miles so it's currently on its third set of carbs.
The tank rusted through from the inside 5 years ago, but the repair is holding OK. The radiator has corroded through a few times, probably because I don't clean it often enough in winter… it's currently on its 4th.
The centrestand cracks on a regular basis: it's on its third now and that's going. I've welded up an old one and added some bracing to strengthen it, I'm just waiting now for the paint to dry fully and the weather to ease off before I fit it.
Both the gear change and sidestand get sloppy due to wear against the pivot, I've replaced and/or rebuilt them with welding and filing over the years.
It's stranded me just once in all this time: the sparks died due to a chafed wire near the ignition unit.