Multitasking to come in iPhone 4.0 software

According to several sites on the Internet the general opinion seems to be that in Summer version 4.0 of the iPhone software will be released and will include multi tasking capabilities. This will extend beyond the core apps to allow concurrent execution of 3rd party apps. Sounds good to me. 

The image above is a good representation of how the screen could display your running apps and allow you to switch between them. Power consumption and available memory are concerns with running several things at once. Plus the potential for Spyware\Malware being able to "lurk" in the background is now a threat. I for one will be keen to see how Apple handle these issues. I expect there will be a maximum number of apps that can run concurrently. Will my iPhone 3G be able to cope with v4.0 software and multitasking or will I have to get the next iPhone model which will probably have more memory a faster processor and a better battery (I hope!).