Is this likely to cause problems with network loops?
If you have portfast enabled on every port and your users have access to hubs then there is a higher chance that loops occur. It would only take a second connection from your switch to the same hub and you have a loop.
A loop is not a local problem because it could affect the your whole spanning tree because the affected router is too busy with it's loop which in turn could cause new loops, even in other vlans.
Better protect the users against themselves. It's not worth the risk. Also, with portfast and a hub you only save yourself 30 seconds when you connect a hub which is connected anyway all the time.
Cheers,
Danny