<p>After reading many of the replies to <a href="https://stackoverflow.com/questions/244302/what-do-you-think-of-the-new-c-40-dynamic-keyword">this thread</a>, I see that many of those who dislike it cite the potential for abuse of the new keyword. My question is, what sort of abuse? How could this be abused so badly as to make people vehemently dislike it? Is it just about purism? Or is there a real pitfall that I'm just not seeing?</p>

Some see it as a tool that will be abused.  Like "Option Strict Off" and "On Error Resume Next" in VB which "pure" languages like C# and Java have never had.
Many said the same about the "var" keyword, yet I don't see it being abused, once it became understood that it wasn't the same as VB's "Variant"
It could be abused in places that lazy developers don't want type checking on classes and just try catch dynamic calls instead of writing "if blah is Blah ...".
I personally feel it could be used properly in situations like
this
recent question that I answered.
I think the ones really understanding it's power are those heavily into the dynamic .NET languages.