[freddystone]

Samurai is 侍. It's a Japanese word and it has a standard Japanese character. I've never heard of anyone reading a different kanji as samurai, and it makes very little sense to me that it could happen. I certainly doubt you could find many/any Japanese people who would look at 士 and think of samurai.

As for "people who do kendo", I've never really heard anything BUT kendoka in Japan, even for my students. Obviously they get the obligatory 選手 (senshu) tacked on after their names in tournaments to designate that they're "competitors", but when people express that they do kendo, at least if they're serious enough to go around expressing it to people, they just run with kendoka to my knowledge. To my knowledge, it's "professional" connotation isn't any stronger than what you'd get in English if you just said "I'm a kendo player." Note the use of the noun. "I play kendo" is more casual in English, and 剣道をやっている (kendo o yatteiru) is also more casual in Japanese.

Kenshi sounds very strange to me, probably because it's something you mostly here in period dramas. Kenshi are people who go around and fight other kenshi, or at least that's the clear impression I have.

I have no idea why the people on aiki-web have a problem with the term aikidoka, since that's what they are.