I'm planning to buy the Motorola DEFY. I tried it out a demo piece at a store .... It seems to have a vertical scrolling screen with icons as well as a set of horizontal scrolling home screens. While the horizontal scrolling seems snappy, the vertical scrolling seems laggy. As I install more apps, will the vertical scroll lag increase further. What's the point of having both those screens anyways ?
I assume you're talking about the home and launcher screens.
The launcher is exactly that, a place for your to launch apps from, while the home screen can be populated by shortcuts, folders, and widgets which make content richer and more accessible.
Perhaps a defy owner may be able to suggest a reason as to why there might be lag and what to do about it, but it might just be a bit of struggle for your phone to load all the apps you have, which is dependant on memory size and cpu speed.
Perhaps a replacement launcher would be faster.
The top two seem to be ADW and Launcher Pro, of which I think Launcher Pro might be marginally faster. You might also want to try Go Launcher and Zeam. Do some research and testing.
As well as being faster, their are often highly configurable. For instance, the feel of the native launcher on my Samsung Galaxy S2 is very 'tactile' and 'organic' despite the power of the handset. However, ADW allows me to set the speed of the homescreen and appdraw so that it is snappy as hell. I can also create differing app draws, excluding unnecessary apps and allowing it to load faster.
What you are describing as the horizontal scrolling is the home screen. It's there to hold shortcuts to apps and widgets. Think of it as your PC's desktop.
The vertical scrolling list is the list of actual applications that are installed (like opening C:\Program Files). When you add new apps, it might take a second or two for Android to load their icons into the cache. So long as you don't install hundreds of apps, this shouldn't get exponentially slower.
I suspect that demo unit probably needed to be reset since dozens of people handle it every day. I haven't played with the Defy specifically, but I have a wide selection of phones running different OSes at my desk and none of them are terribly slow in the launcher app.
I just bought the phone yesterday after reading a lot about it. My phone doesn't have any lag in the app launcher(the screen with the shortcuts for the installed applications, vertical scroll) and has about 50 shortcuts and it's quite responsive.