Hi Zoslen; welcome to the Thorn Cycling Forum!
I owned a Sherpa for about a year and now the same for my Nomad Mk2. I've found the paint to be very durable except for the dropouts, as both Rual and Geo' noted -- it came off in huge flakes there*, but it doesn't matter as the dropout faces are stainless steel and not subject to rust. The paint adhered flawlessly elsewhere on my two bikes and they proved o be very resistant to chips and nicks.
I am big on touching up nicks on all my bikes, as with either wet paint or powdercoat, I am reluctant to expose bare steel to the elements, though some of our Forum members have had no problems doing so (depends on environment I think -- salted roads and coastal climates are Bad). I believe it is more important to touch up scratches in powdercoat to prevent any rust from tunneling under the melted/fused plastic that comprises the powdercoat. This isn't limited to Thorns, but seems like a Very Good Idea on any powdercoated bike frame to prevent any rust from spreading unseen until it becomes a Real Problem when finally noticed.
When I ride the Nomad unladen, I often mount by swinging a leg over the saddle. When carrying a load atop the rear rack, I tend to hold the handlebars and saddle, tip the bike at an angle, and "step through" by putting my foot over the top tube. I was concerned my foot might someday scrape and scuff the top tube and cause unsightly scratches, so I decided to be proactive and placed a length of matte black windshield trim tape atop much of the top tube (it is a very good match for the matte black paint). The leading edges of my painted crank arms often get peppered with gravel, so I may add little tape shields there as well.
As for the cable guides, the ones on my Nomad Mk2 are stainless steel so even if the paint wear through, I won't have to worry about rust.
Best,
Dan.
* I think it is a combination of the high clamping forces and embossing of the knurled backside of the q/r and axle locknuts that cuts through the powdercoat, combined with the sliding/scraping action of the axle locknut faces when removing/reinstalling a wheel that causes the finish to flake off the dropout faces. Again, not a problem because the faces are stainless, and not even unsightly 'cos the hub q/r covers virtually all the bare metal.
