Galaxy S.
Hardware:
- Has super-amoled display. It is very bright and vibrant. Makes iphone4 display, although sharper due to higher resolution, looks pale/pucat.
- 4" screen, slightly larger than iphone4
- Gorilla glass: Scratch resistant screen from Corning, which I believe is better than iphone4.
- Has front-facing camera too for video chat

Software:
- It comes with Android 2.2 (Froyo) with touchwiz skin.. Nice, but not as polished as ios
- Android market: In terms of apps, you can find pretty much everything. Number of apps in the appstore/market doesn't matter much
- It has unobtrusive notification system. Unlike iphone that hinders from what you are working due to streams of notifications.
- Unlimited customization: Steve jobs dictates how your phone looks like. If you want to be different, either jailbreak or put on a casing. With galaxy s, you can customize a lot of things: Home launcher, background, icons, etc
- Widgets: No need to open each app like facebook and twitter separately to see updates. In galaxy s, you can see updates straightaway from your homescreen.
- If you are user of google, you'll find galaxy s more appealing as their software is more up-to-date than iphone counterpart. Example:
  - Gmail app is excellent
  - Google maps: can see 3d buildings of new york/washington dc etc. Google maps in iphone is outdated.

Usage:
If you are more on productivity, like multi-tasking, choose android based smartphone like galaxy s
iOS has the advantage of more 3d games and more polished user interface.

Galaxy S: No need itunes and usb cable to sync with your computers
iphone: needs cable and must use itunes. but itunes give access to a lot of multimedia contents.

Philosophy:
apple: makes everything easy for you by limiting your options and choices
android from google: gives unlimited options for you.
Feel free to clarify