My main problem with multitasking on iOS is that there isn't a good startup service implementation -- so for example if I restart my phone and don't open Google Voice at least once, I won't get push messages from it.

However, one of the reasons the platform performs well (esp. with battery life) is that the OS can kill a background process at will, and apps expect that and are usually designed to handle that gracefully. Hopefully there's more work coming to make this less of a trade off, especially as new phone versions have more resources.