After looking at the options, I found that the most infrequent update is every 3 hours. Why can't we set our own update frequency? I personally am getting annoyed by the "checking curse addons" appearing all the time. Surely this would be a sensible option? I can't see anyone that would want updates this frequently except those who are hardened gamers - which I'm not.
If there's not going to be any hope of this happening, then I'll just close the program and only open it when I decide a check should be made.
But apart from this small missing feature, I find the curse client excellent!