iPhone 4.0 beta walkthrough video in English

My favourite feature in Iphone SDK 4.0 is multitasking feature. I have read it on developer.apple.com but dont know how to use it in my xcode.
Actually I am interested in running more than one application at the same time, i.e one should run in background continuosly untill i stop and other should be run by user.

what about multiple signatures - while the one inbox is ok for some (i like having them separate). That said, multiple signatures would be EXTREMELY HELPFUL!

I am still waiting for a bullet-proof reminder system. I want to be able to snooze calendar events with one tap. I also want to be able to set up default settings so that I don't have to enter the "one hour before" each time. Finally, in Exchange you can only have one alert. Do any of the 4.0 features help with these concerns? Or do they make it easier for third-parties to make such an app?

Is this OS 4.0 update now available?

beware if you do the beta upgrade. it has bugs. some apps don't work. it is a complete pain in the ars to downgrade too. you have to terminal into your phone to get it to downgrade back to 3.1.3 or lower. spent a long time last night trying to figure it out.

The "iphone 4G" probably wont be called 4G to prevent confusion as it will still be on 3G networks. It will most likely be called the iphone 4x or x4 to match the name of the new cpu.

yeah, I think this update is apple's innovation, and there are many folks looking forward to it. Guys, if wanna learn more info about iPhone, iPhone 3G(S), its video & audio formats, review, tips and tutorials, can go to this spot: http://www.ifunia.com/iphone-column/index.html

I'm using the 4.0 dev preview on my 3GS presently. I've found a couple bugs regarding the inability to change the default raindrop wallpaper, and the lockscreen changing to album art of the last played song on the iPod app, regardless of whether or not the app is still playing or even open.

Those two things are kind of annoying, but other than some apps not playing nice with 4.0 and some freaking out at the multi-task, things seem OK. Multiple Exchange servers and threaded email conversations are nice.

In my opinion, Apple really missed the mark by ignoring ring/notification/data profiles. They simply will not be taken seriously in the business space until these issues are addressed and included -- that means the ability to swap the ring profiles based on calendar items, the ability to change notification sounds to something that doesn't sound like a cartoon sound effect.

They're also hurting themselves significantly in the productivity space by leaving a huge swath of empty real estate on the lock screen. This is no longer acceptable if the device is to be taken seriously for business.

Overall a good update -- but they really need to take a step back and address some fundamental pieces of functionality that they've ignored.

My missing features:
1.) better notifications… "Droid Does" just add it already.
2.) search on a web page or in an app. I opened a word doc yesterday to try to find a specific piece of info. Try finding a single word in a 20 page document on the iPhone. On my pc it takes 2 seconds. On the iPhone it took 5 minutes.
3.) still can't open shared calendars on Exchange. What good is being able to schedule appointments when you can't see anyone else's schedule?

Will we ever be able to add custom tones with text messaging. Getting really tired of the 6 available. Also, any chance of a custom email sound?!