I agree it's a local issue, but it's something wrong with IDT and not the machine. When I'm writing a formula in the SQL editor (nothing fancy, just writing a formula), the InformationDesignTool.exe process spikes one of the cores in my i5 machine to full usage and each keystroke takes almost half a second to appear onscreen. Comment #5 on this post also reports excessive CPU usage.
I'm also at a loss as to why IDT needs to fetch data from the server when I merely click on different objects in the business layer tree. The application stops responding momentarily and I can see in Task Manager a slight increase in network traffic. I would expect all this data to be local on my machine from the moment I open the universe, or at least cached after the first click on an object, but clicking back and forth between the same objects incurs the same network traffic and application unresponsiveness.
This is on SP7 patch 3, connecting to BW cubes with a JCo relational connection.