...There are a number of options for rooted and tweaked builds of the OTA update already, but if you want a fully stock phone that's simply rooted and nothing else, while flashing as little as possible, you just need to Odin cwm, boot directly into recovery, and flash the generic su binary (.zip package found at http://androidsu.com/superuser/). Then simply reboot. The stock kernel will overwrite CWM with the stock recovery, so it will appear fully stock even to an advanced rep who may check the recovery (which is HIGHLY unlikely), but you will have the su binary. Then just get Superuser (and also Busybox Installer) from the Market and you're good to go..
For those of you who would like to follow this rooting method, one tip I can give is that the su zip will not stick if you do not manually mount /system in recovery first. That gave me some headache after flashing su about 4 times before realizing my mistake. Also, the link above also has the full Superuser package as a zip, with the su binary and the Superuser apk in one. Might be a bit faster to kill two birds with one stone with the full zip. Hope this helps.