iOS 4.3.1 less efficient with memory management?

On my iPhone 4, I usually keep the same eight programs active in my 'multitasking' drawer at all times - Safari, Facebook, Engadget, Mail, Weather Channel, Sportacular, Messages and Phone.

With previous versions of iOS 4, I would be able to cycle between those programs with little to no difficulty. As of late, I've noticed the phone having difficulty keeping Safari tabs in memory and having to reboot 3rd party applications like Sportacular when I switch tasks.

Using the app Activity Monitor Touch, I've seen my available memory drop as low as 30MB, while on the prior versions of iOS 4, my phone would stay at least above 100MB with those same eight apps in the multitasking bar.

What's going on here?