Hey guys. Yeah I got my set from the US. My friend went to Best Buy to queue before he came to Singapore for Christmas.
The charger etc all work in Singapore. You just need to buy the adapter plug. The only thing of course is warranty isn't in Singapore, so you take that risk when you buy.
OTA updates work fine, I got my update to 2.3.1 already.
As for comparisons between SGS and Nexus S, I would say if you have the SGS don't bother to change. It's the same phone! My wife has an SGS and the only difference is that the colours on the screens look slightly different because of the calibration i think.
Nexus S is thicker but narrower than the SGS.
Once SGS gets gingerbread there won't be a difference between the phones, except that the SGS can still use additional SD card, and that the SGS has 2GB ram to store apps..I think the Nexus S is only 1gb ram.
I would only recommend Nexus S if you are coming from an older phone like the Motofail phones, or a really old android like HTC hero or something..
If you have a Nexus 1, Desire, or SGS there is no point in getting a Nexus S unless you have cash to burn..
I have both Google Nexus one and SGS...both stock to stock comparison...Nexus One day to day experience is so much better than SGS..SGS needs much more of my time to try out different ROM/tweak to get it to work properly...the additional stuff putting in by Samsung is suck..Google stock keyboard is 100x better than the stupid samsung keyboard. GPS not working, system suddenly lag..all not exist on Nexus one but uniquely Samsung..
Google is strong in search function, Samsung make the default search bar not available..highly discounting the user experience.
I am fan of Google Native Android system with reference to my experience with Nexus one and SGS(middleware making thing worst off)...thus I believe Nexus S will be a good phone with combination of ..good hardware(good video/audio ) from samsung and good/reliable software from Google.
My Nexus S (USA set) already reached Singapore however i am still out on holiday..looking forward to seeing my Nexus S..on 4 Jan..
The main problem of Nexus One is small Rom for program installation...which i have to constantly optimizing the program installation space..between internal/External SD-card.. I will only regret if Google officially enable mapping larger memory for program installation on Nexus One on the coming update..

Hopefully their company isn't closed for the holiday as I ordered it a 2 days back. I dunno about holiday periods such as this week, but on average it takes only a week for the protector to be here.