Before you flame me, I have to give you some background:

* I've never owned an iPhone, but have owned iPod Touches (I can't stomach iTunes and prefer MSC devices that play a multitude of codecs).

* I loved my Nokia N800 & N810.

* I am not programmer or developer.

* I desperately want to love the N900.

So...

Any touchscreen owner who doesn't own an iPhone has stared longingly at the fluid scrolling and touch-response of an iPhone.

At this point in time, the iPhone gives the finest touchscreen experience of any device I've seen (and I've seen a lot). Why is that? Are Apple engineers better than Nokia engineers? What do they know about programming a UI that no one else has truly figured out?

I believe that today a phone UI experience has to equal that of the best product out there. The N900, as we all know, doesn't. It's true the N900 runs rings around the iPhone in terms of other features - but much of that is moot if the experience isn't fluid.

I am sure that people at Nokia HQ have a couple iPhones around that they can use as benchmarks. What would possess them to release something that doesn't equal that experience? The N97 was a joke and the N900, while awesome, doesn't have that "magic" (in regards to the fluidity of the UI).

So devs and programmers, explain to me why Apple is able to create that UI and Nokia (and Samsung and LG and HTC, etc) aren't. Are they magicians? What is the secret?

Again, I am not talking about copying the graphical interface, just the fluid, effortless UI experience.If Nokia could replicate that UI experience onto the N900, it would incredible.

Please enlighten/educate me. Don't flame me or tell me to buy an iPhone, I don't want one -- but really do try and explain to a layperson why their UI is so damn fluid.

1. Their PowerVR GPU is faster than the one on N900
2. Their screen runs at half N900's resolution
3. Their OS is somewhat optimized for singletasking with plenty of resources spared for UI (with some background-enabled apps)
4. I bet 'make the UI as fluid as possible' is one of Steve Jobs' prime directive to his team. So this has always been optimized and yet optimized more. It's always been like that since v1.0.

I also think that capacitive screen have something to say

So if the iPhone was to run at the N900's resolution (with the current chipset) it would stutter as well?

Out of limited resources, Apple chose to make the UI fluid, at the expense of things like multi-tasking.

Out of limited resources, Nokia chose to make features like multitasking work, at the expense of things like UI fluidness.

Eventually, the hardware will become powerful enough to support both. Then you will see the iPhone multi-tasking and the N900 successors with a very fluid UI.

If you have been following the hardware market, we are very quickly reaching that point.

1. capacitive screen , easier to go from screen to screen cuz it doesnt require pressure to switch screens
2. the UI is so plain and straight forward on the iphone, its just home screens with no background or anything... besides icon thats about it nothing else.

Or, jailbreak an iPhone, enable multi-tasking on it, and see how it fares.

Dont forget that Apple has been in the UI game since 1976. Nokia were not even making phones or anything software related. Apple's UI Look and Feel expertise has a.ways been its USP in the face of Windows domination. However, I am more impressed by HTC, Apple is kind of stale these days. In any case I prefer the N900 to all the iCandy out there - function over form.

How does it fare? Can someone comment on this?

Quite likely. It's the same for 3D games on the PC, lower resolutions can maintain higher framerates due to having fewer pixels to render. Higher resolutions require more powerful graphics cards to maintain higher framerates.

The biggest fluidity-killer is background processes (almost always Maemo system processes) that grab a chunk of the CPU to perform some action. Modest is very, very bad at this, especially when responding to a mail notification with a couple things are going on. This will be somewhat resolved once multi-core chips are more common, however.