Hi jonny, i bought a gutter vac august last year, to add gutter clearing to my services, as like you i was been
 constantly asked do you clean gutters.
 Like dazmond & smurf said it can definitely be hard & dirty work, most of the gutter jobs i get haven't been
 cleaned out in years so take longer to do, i rarely get an easy one.
 You have to keep an eye on the silt in some long overdue jobs, as it can completely bung up your poles  &  hose if not rinsed out regularly with water sucked from a bucket, you will soon realise there is a lot of silt when your  poles quickly become to heavy to comfortably work with, ( i use Carbon Poles too).
I carry a ladder because occasionally i will come across big lumps of turf or weeds & sods, that would be easier to run up the ladder and do by hand. i only bring the gutter vac out on prebooked jobs, but it is a bit 
of faffing about loading onto your van with a ramp i had made, then unloading at the job, sometimes when I've finished a job i can get rid of the waste using the customers recycling bin, a lot of times not, then struggle
to get a nearly full gutter vac up a ramp and back in van, then get home clear out the contents into my own recycling bin, then wash out hose & poles ready for next job. I'm still building my window cleaning round after
three and a half years and the gutter clearing definitely brings in extra money, but saying that i will eventually 
drop the gutter clearing when my round is big enough because it is a PITA.
Regards
Lal