For several months I have suffered from a very slow “save as” dialogue in many applications. It would often take 20 seconds to render.
The opinion on the Internet seems to be that Windows 7 is looking for possibly non-existent shares on the local network. A diagnostic test that this behaviour is that the fault will not be present if booting into safe mode without networking.
One user suggested deleting non-existent shares from your registry. However this advice is not very useful if you don’t know the names of them. Another user suggested turning off network discovery and this worked for me. The great benefit of this approach is that it is quickly tested and easily reversible.