> I don't have to lose time writing types

In C#, I write type names when I declare a type, when I create instance of a type, when I declare method argument or return type (which you would probably do even in a dynamic language as a comment - you don't want people to have to go through your code to figure it out themselves, right?) and when I declare a collection of that type. Out of all of these, only the last one seems as "wasting time", because if I declare a collection and instantly use it on the next line, the reader can probably infer what type I meant to use - but in all other cases, not writing types would make the reader's job harder, not easier.

Don't the same principles apply when you're working in a dynamic language?