We've heard before that, among other things, iPhone OS 3.0 would support quad-core processors. Of course, we haven't seen these processors yet, but now ST-Ericsson and ARM have announced they'll be giving a private sneak peak at one at Mobile World Congress. (Via MacRumors):

The technological breakthrough is the first of its kind and is based on the ARM(R) Cortex(TM)-A9 multicore processor, which represents a significant leap from previous generations of baseband/application processor architectures by providing unprecedented levels of performance and power efficiency.

Combined with previous rumors of OpenCL support allowing the faster, betterPowerVR graphics cores to boost general processing as well, and 802.11n mobile WiFi chips future iPhone generations could be, as Steve Jobs is so fond of putting it, real screamers.

Better hardware (especially more RAM) could, of course, encourage Apple to allow more 3rd party multi-tasking. Maybe even make the leap to iPhone HD? (In a matt black finish?!)