My university usually releases a site installer with major versions of EndNote. However, from time to time you need to update EndNote to make it work decently with a certian version of OS X or Word. Quite often the program itself gives a notice about an update being available.
However, the problem is that downloading the~42MB update or so from endnote.com is very slow. This can take anything from 10 minutes at best, to 30 min. in a worst case scenario. It has been like this for a long time. I am pretty sure the updates were downloaded faster at a certain point in time. Are the downloads throttled?
If you do the download inside EndNote itself, you also have no idea about the progress of the download, which is quite frustrating. I usually resolve to download the update manually first, like this one: