I have to complain about the Dojo Toolkit (Considering the project I am using this for). It has the worst documentation and API guides I have ever seen. The documentation (called the Dojo Book) has an unnecessary complex structure to click through and its contents are wrapped around examples that are so overly complex that you click away the pages when they get smashed at your head.
The API too, has no clear structure and hides its contents behind cryptic names such as "dnd", "fx", "rpc". Descriptions of the functions sum to very small sentences and additional options are listed without any description at all other than a link to where they are defined in the project. There are no short examples given to any function like jQuery does.
In general I think the Dojos Site is too complex and hard to navigate. The layout seems to change massively on each click and you it is hard recognize common patterns. Dear Dojo Team, please make your project more accessible!