It is understandable why iPhones did not allow multitasking from the start. Implementing and enforcing multitasking while keeping device responsive is hard. Users don’t look kindly their devices becoming unresponsive, while slower processor chokes under loads from multiple different processes.
N900 works great for the most parts, but get really annoyingly sluggish in few cases. My favorite case is going out for a run and trying to map the route with eCoach, while also listening to music with MediaPlayer. I usually have music already playing, when I step out from home and start eCoach. eCoach tries to find GPS-signal and at the same time opens internet connection for map data. When internet connection gets opened N900’s communication tools start to make contact with IM networks I have configured to be used. And then the device becomes unresponsive for some time. As I am a geek and a programmer, I know or have some kind of mental model on what is happening in the device – and therefore just wait patiently, instead of furiously trying to press keyboard or items on display — but normal user would most likely be rather frustrated by the experience.
Haven’t tried how well Android’s multitasking works in real life use, but would like to hear experiences.