I think the "corporate effect" is mostly on IE6. I've seen that people who have a choice to switch from IE6 usually do, but they switch to IE7, not Firefox.
For example, my company gets a ton of hits from IE; about 50% IE7, 25% IE6, and 10% Firefox (our software is for Windows, so we see almost no mac users). The only one of those that drops considerably over the weekend is IE6 (by about 10%) and IE7 spikes nearly as much (8%).
For example, my company gets a ton of hits from IE; about 50% IE7, 25% IE6, and 10% Firefox (our software is for Windows, so we see almost no mac users). The only one of those that drops considerably over the weekend is IE6 (by about 10%) and IE7 spikes nearly as much (8%).