MobileSafari has fantastic debugging support when paired with Safari 6 on a Mac, and I think there's a similar feature available for Chrome on Android. Here's MobileSafari's waterfall for stevesouders.com: http://rpetri.ch/db/stevesouders.png

It's probably worth noting that Network Link Conditioner (on OS X) could probably be used as a substitute for a hardware mobile hotspot, if you want to simulate 'poor' connections.