I've read somewhere in a manual for a washer years ago to always pressure wash at an angle or dirt can be forced into the paint, but I've never known of it actually damaging paint work.
As for the foam lance, I got a karcher washer and lance over Christmas with karchers own brand foam solution, I tried that combo once!
Now using karcher washer, the famous 'eBay lance' and angel wax fastfoam (ATM)
FYI stay away from karchers own foam solution, it's very chalky and doesn't smell very pleasant.