I'd hate to play 3.5e without my laptop at the gaming table.
My problem isn't with the modifiers per se, it is with the knock on effects and the overlapping/stacking thing.
Penalty to Strength? That affects melee attack and damage (but not missile attack) and carrying capacity (can you move in your armour?) and several skills and...
Raging? That affects strength (see above) and Con (fort save, hit points, endurance checks) and AC and will save but only against certain specific effects.
The psychic warrior who uses their version of enlarge, and offensive precognition, and defensive precognition, and prescience, and a couple of other buffs is bad enough, but when he gets hit by a targetted dispel that takes down some but not all of the effects, and he is then inspired by the bard but targetted by an enemy prayer spell and hit by ray of enfeeblement...
I'd hate to try and manage that without it all calculated into my spreadsheet.
I've mentioned it before in other threads about what makes 3e more complex in my eyes; I think the plethora of transient modifiers with the minutiae of overlapping and stacking details are a big part of it. I'd almost be tempted to say that large numbers of transient modifiers is THE distinguishing feature between D&D (and by extension, d20 games?) compared to the other RPGs that I've had experience over the years.
My RPG experience is far from exhaustive, but I know that I've had lots of fun with RQ, Traveller, 1e and other games where transient modifiers were not such an integral part of the game.
Cheers