Eighty-one. I have 81 esms and esps, according to the number of Form IDs in OBMM. Not all of these are active all the time though, some of them only get used for certain characters.
Come and think of it, I actually have more than 81. It's hard to say. Some mods don't include esms / esps, some of them will modify the game hiding in background. I estimate I've got another 10 of these, perhaps. So approximately 90 overall. That's twice my 'goal' from a year ago. I think I started Oblivion on PC almost a year ago.
To think it all started with Snaat Rayag in the Tutorial dungeon on my old PC (made for office work, not gaming), and I had no idea why the dungeon was so bright.