2001 is a good model (I have the same, so I'm not biased

). These are ABS brakes but not servo. Personally I like the ABS but some will differ (got me out of a cack handed jam yesterday thanks to a nice attractive lady pulling out in an unattractive SUV).
Later models fitted with the servo brake system report some problems and the brakes are not effective without the engine running.
The value of twin spark plugs on later models is also debated - I have always found single to be fine and saves double the cost of the plugs. Check for staining on the right side of the gearbox as some models had problems with fuel leaks. This was easily solved, usually under warranty or recall but good to ask at this point if recall work was done (front fork brace and fuel lines from memory).
As you know doubt know the standard headlights are rubbish, so if there is a HiD upgrade this saves a few pennies. If it has a huge aftermarket top box, check for cracks in the frame under the passengers seat - unusual but it does happen if people are on rough ground and load up the top box. As you know, rattles and clatters from the engine are normal, so long as they are not excessive (very subjective here...). Check for oil leaks around the drive shaft, particularly the lower boot as this can be expensive.
In many ways, the bikes a pretty bomb proof and if it is a good, clean running model with relatively low miles it's hard to go wrong. Even a little corrosion or pitting on items like the front lower forks is not the end of the world as it is usually easily cured or cosmetic and makes a very good start to the bargaining process.
I'm sure others will be along shortly to add comment.