As the dialog says, it's fetching tree conflict information. This means that the update caused a tree conflict which you have to resolve.
To help you with resolving the tree conflict, svn tries to fetch additional information about that conflict. But it has to contact the repository to do so.
Depending on the version of the svn server this can take a very long time.
Of course, you can cancel that info-fetching. But then you have to figure out yourself why the tree conflict happend without additional info.
And yes, most users won't need that additional info to resolve the conflict.
Stefan