I used ID next QuarkXPress, and I'll tell that Scribus is similar and simple program, so I don't expect any problems for person which go from ID, Quark to Scribus.
ps
I noticed that free programs today are very good and may be substituted for big professional programs.
However, the big manufacturers do not see it yet. Gimp, Krita, Pixelmator, Inkscape, Karbon, Ghostscript, psnup, Scribus, Vectorian Giotto, imagemagic, sk1, Kdenlive etc for person which know this tools very good, expensive programs are not necessary. Perhaps some people will be quit from for example subscription, and will elect programs like Scribus, Krita etc.