I've not had any problems with 600 engines, had a few old Triumphs where I had to put the front wheel against the wall and kick over with the clutch in and had a Caterham 7 car with a ford Xflow engine and Mexico gear box that had to be bump started and driven hard with the clutch in to release it.
My 350 is the same, I just pull in the clutch lever and kick it a couple of times, it frees off pretty much first or second kick. It was worse, and at traffic lights it would kind of snatch when in gear and the clutch disengaged. I removed the plates and cleaned them with brake cleaner, much better. The bike had been standing for a long time before I got it, I reckon the oil impregnated in the friction material for so long left a residue which causes the plates to be sticky. On other bikes it's taken quite a few strips and cleans before it is 100%. As I said,when cold and before starting, just kick it over with the clutch lever in. Oh, and the ignition off!.
Folks - thanks for all of the answers. Once I've finished fixing some cracks in the fairing I'll get the clutch out this weekend and take a look at it. Next question (and there'll probably be more...) - do I need any special tools? I know that the manual says "yes", but quite often people have found another tool that does the job.
Progress: the clutch is out, and it's been pulled apart. Nothing looked too amiss, so I cleaned everything up with some white spirits and started checking and measuring...
The plates seem flat - I put them on a piece of glass and tried to spot any gaps. The basket/hub all look ok, with no notches or significant wear marks. However most of the clutch plates appear to measure between 2.5 and 2.6 mm thick. The manual mentions replacing if 2.7mm or less, so my next task is to try and get some new ones.
Its been a while since I bought any parts for the beast - so can someone point me towards a reputable supplier (before I start getting lost in the dark reaches of the internet?).