Dojo pros are IMO the following:
1. Provides a simple DOM query functionality, like jQuery, ex:
dojo.query(".disableAble").style("backgroundColor","gray");
Have really smart loader, which can pull in all classes at once, incrementally or at your own choosing. Also correlates with the build system where you pick your menu and compress, inline, et.c.
In my opinion the most important thing; A full client-side hierarchical widget system that is super-easy to extend, with support for DTL client side templates. Forces you to modularize your code and utilizes Dojo's own build and load system for custom widgets as well.
Almost all things that people write for Dojo become part of the 'official' build, under the dojox (experimental) folder. Many other toolkits have a lot of variants of the same widget making it hard for users to choose the right one.
Cheers,
PS
http://unclescript.blogspot.com
