Recently a user complained at my desk about his logon times. When logging on to a new pc, he often had to wait 15 minutes before he got his desktop in front of him.
Typically, this means A) a slow network or B) an enormous profile.
In this case, B was the case.
Some investigation pointed out the Dropbox folder to be 14GB (and growing!). To avoid these kinds of problems, it’s best to exclude such directories from roaming to the network by using a group policy.
In the GPO, go to User Configuration, Administrative Templates, System, User Profiles.