It's been changing for me lately, especially since I've added more characters to my roster. Usually, 30 tags is a good number for me if I want to be really comfortable doing tags and whip them out within seconds of each other. With seven characters though, the only way to get 30 tags or less is if I sit down for two hours and methodically work through my inbox.
Currently I can deal with about 50-60 tags (that's been the norm for me) though I prefer less. Past 80 I tend to just curl up in a ball and refuse to look at my inbox for a couple hours. I think if I ever hit 100 I would actually cry. :'(