An awful lot of the basic ID interface is similar to Illustrator, especially text formatting and the basic drawing elements. If you're familiar with Ill, the basic pickup is a dream. I went from Quark 4 to ID3 with no problems at all, although I never really liked Quark - preferring Pagemaker if I could get away with that. I knocked out a 100 page program for a pro sporting event in 3 days within 2 weeks of buying ID. It used to take me twice that time in Quark.
If you're going to go ID, you should consider the whole Creative Suite Pro package. Adobe offers an "upgrade" from any version of Photoshop for $750 - giving you Photoshop, Illustrtator, Indesign, Acrobat Pro, and Golive plus a binck of Opentype fonts. That's a pretty good deal. Even the full prics of about $1200 is pretty good. When I bought it last summer, it also included this Pagemaker plugin pack which includes InBooklet SE - a basic imposer. I find that Acrobat Pro is really useful. I rarely use ID pdf export for final print pdf creation because printing a postscript file from ID gives you a lot more options than a straight pdf export.
As far as the printer goes, if he's not able to use ID or pdf, he's going to lose business and that loss is going to increase. An awful lot of user, from individuals to major corps and ad agencies are adopting ID. I've found some printers who can't handle ID but can handle PDF or they can't handle PDF but can handle ID. I haven't run across an (in New York) who can't handle either.