Ian Cooper has a good talk that's relevant to this blog post. It's called 'TDD, where did it all go wrong?' and a recording from NDC 2013 can be found here: http://vimeo.com/68375232
Tools like Typemock helps you make bad decisions that you will regret later on...
Isolating things is very important to make it easier to test, and lower the risk for tests to break when you change other parts of the system. Some times isolating one part from another is hard work. Typemock makes it easier, but in the same time it ties you closer to the part that you are trying to isolate from.
e.g. a database. You want to test something that eventually should store something in a database. You can either make a thin layer abstracting away your database so that you can test the functionality without depending on the database, or you can make a tighter coupling to the database, and use tools like typemock to get rid of it in test mode. If you want to change the way you store data, you now have production code tightly coupled to the current storage strategy AND tests tightly coupled to the current storage strategy...
Typemock can be of great help some times, but really you should strive to find better designs instead.