Tread the line between consistency and variety. Contrast increases impact. Stand back and look at the document as a whole. It is hard to read. Limit fonts to 2-3 per piece.
White space provides contrast and allows the eyes to rest.
Jono pointed out that although many companies are using Windows, most design companies are still devoted to Macintosh operating systems. This is not an insurrmountable problem, but the names of fonts may not translate exactly, so make sure to deliver a hard copy of data as well as on a disk. Oh, and a special thanks to my little color desk-jet printer, which worked so hard to produce all 450 of those invitations. All rights reserved.