The sorting of tags is still not what I would expect in 5.1 SP1. It seems the sorting is done by the first letter only. See what happens in sf_tag_sorting.png
Categories sorting is strange as well when you want to pick a parent categorie. Created the Schuljahr categories one after the other 2005/2006 then 2006/2007 then 2008/2009 but it also seems to be sorted in some other way then expected.
Thats another thing I would like to see fixed in 5.2
How do you filter through tags when you have a couple of hundred? It would be nice if you had a dynamic pulldown where languages is for filtering or a 1, a-z navigation like you have on mobile cell phones phone books.