Yesterday I used the ipfw command to run our product in "slow motion" to spot loading order and if animations started at the right places. Discovered alot of stuff that needs fixing. The ipfw command is for trottling bandwidth, and great for product designers like myself :) I'm sure it has other uses as well.
OS X has a useful Network Link Conditioner utility. It has built-in profiles such as lossy 3G connection, average wifi connection, good wifi connection etc.
You have to have Developer Tools installed. I am at work right now, not on a mac, but I will try from memory. I believe you get it from Xcode > Developer tools > Get more tools. I don't recall the exact menu tree but I am sure you can google it.
After that, it's integrated into the System Preferences panel. You simply pick which network conditions you want to simulate.
I think it's also possible to launch it from the xcode Utilities folder w/o installation. Sorry I can't be more coherent w/o my machine in front of me.
