Hello,
Im new here, but I had a IP4 for a few months (august and part of july) like the OP.
I switched it for a SGS + some money I needed. What I really miss is the iphone 4 steel border look, it was really neat. The SGS looks like a 3GS tho, altough the plastic seems higher grade to me (higher fingerprint magnet grade too rofl), quite often some people told me 'hey you're back with your old phone? did you break your iphone 4 ?" and I went "lol no it's some android stuff i'm trying out".
I still think the IP4 cosmetic finish is far superior, but the SGS is well above "OK" too.
To sum it up. + is pro - con
Stock international galaxy S :
+ Gorgeous screen, the color density (even tho far from the real gammut) make me feel happy every morning, I don't really see a difference with the retina unless I get the phone really close to my eyes, except maybe in the web browser with lilliputian fonts.
+ Screen size obviously, I have rather large hands so it was really a big pro for me, I had much less trouble typing accuratly. Swype is kind of meh, I think it takes some training to type faster with it, training which I don't want to do, however if I have only one free hand swype is really nice.
+ I don't know about you but I loved the samsung media/music player thing, very well done.
+ The godamn drag notification bar and multitasking.
+ Very smooth on 2.1 I didn't try the 2.2 leaked yet.
-/+ GPS issue is there sometimes, for example if you're surrounded by tall buildings it fails, however it works fine once you are driving in open space. I have read on android forums that the issue was already fixed in the very last leaked firmware.
-/+ Copy paste was pure ****, however installing the app "copy paste it" improved the copy paste function over the IP4's one, basically you just draw a square and it copies to clipboard anything that's in it !
-/+ The apps on the market are often ******, but overall if you dig a bit more you can find very good apps that are free. For 10 ****** apps there's always one (often not advertised or featured) that is godly, it takes a lot more time to find the good app than on the app store, however I liked the 24 hour easy app refund if you didn't like an app. Overall I found a good clone of about any iphone app I was using, except for some games like angry birds, which I hope is coming out soon.
+ This brings me to gaming, the SGS is a beast for it, technically speaking the gpu of the sgs is about three time faster than the IP4, however games that are iphone ports are for the moment better optimized on their native device.
- Kies (the itune thing of samsung) is BS. Hopefully I don't need it for anything except firmware upgrades.
- I tried to look on the web for leather cases and stuff for the SGS and man it's like being teleported from a huge mart to your local little grocery store. Much much less choice.
- I had a bit of a hassle to get my protected oldest musics out of itunes with a third party software but I managed to find a free one.
-/+ Touchwizz was quite nice for the transition to android, but it is really lacking compared to iOS, kind of a cheap clone, stock wallpaper and theme looks ugly. However touchwizz looks kind of cool if you find a livewallpapper you like. But that didn't cut it for me, I wanted more. That's why I searched a bit on some android forums and I found an app called Launcher pro to erase touchwiz and gadgets (switchpro, SMS unread count, and another called desktop visualizer that allows to make your own icons out of any image). I'll post a screenshot.
That's all, overall I'm pretty happy with android at the moment, but only because I can customize it at my own will. I really like about android the fact that it is "your phone" not just the very same as your coworker next door with just a different wallpaper. If someday an app similar to launcher pro comes out on the iphone, be sure I'll be back within the hour.
As promised a screenshot of what my desktop looks like (this is the screen of the theme I took inspiration of, it's maker kindly told me how to reproduce a similar layout), I just love the fact I didn't even need to jailbreak the phone to do that. Sorry if my english was sub-par. It's not my native language.