We have quite an extensive description of the Android UI basics in our T-Mobile G1 review, so to keep things short in the Samsung I7500 preview we'll just try and focus on the changes brought by the latest revision of the OS.
The biggest change in the Samsung I7500 Galaxy obviously is the switch from a physical to a virtual keyboard. It does the whole-letter pop up each time you press a key but there's something to look out for - three dots under the letter. If those appear, a press and hold will bring up all available related symbols - the letter with all the diacritics for example. The keyboard also auto rotates to landscape thanks to the accelerometer.
The I7500 virtual keys are smallish - especially in portrait mode - and typing could be very error-prone. Otherwise, the keyboard offers helpful features like a ".com" button when you're typing an URL, or a "Next" button when there are more fields to fill in, with that button changing to "Done" at the end.
You will spot that the Apple iPhone keyboard is physically larger. The larger screen estate surely adds to that despite the lower resolution. But the most important difference with the I7500 Galaxy is that the iPhone keys are more loosely spaced apart.
We've all seen phones boasting on-screen widgets that notify of new emails or display an RSS feed. With version 1.5 on the I7500 Galaxy, Android is trying out an interesting solution to unify such things and make them an inherent part of the interface.
The solution is called "Live folders". The main difference with ordinary folders is that the live folders are automatically filled with content. For example, there's a "Contacts with phone numbers" and a "Starred contacts" live folders. They do what you would expect them to do - they are filled with contacts that have phone numbers or are starred.
Nothing particularly exciting so far, but that's not even half of it. A live folder can be populated with your emails, playlists, an RSS feed, bookmarks and so on. There's a simple API to provide content for live folders. In non-programmer talk, this means it's easy to write programs that stay in the background and fill the various live folders with custom content.
So, it won't be long before Twitter live folders become available, or a folder for your Netflix queue, or just about anything, that can you can make a list out of. We think this is a great way to deliver dynamic content to your homescreen from many sources without it becoming a colorful mess of differently styled widgets.