I ordered one online. The main reason I was disappointed in it was that there is a major problem with my phone regarding the sensitivity of the back button. It often takes several attempts to get it to detect a button press. I have the 9020T model, so this probably won't be an issue with the Vodacom variant, but I've seen many people complaining about the same problem online. I'm still running 2.3.1, because no other update has been available via the OTA updates yet (even though some people are as far along as 2.3.4). Apparently 2.3.4 fixes the back button issue, but I'm yet to see this myself. You can update manually yourself, but I'm not keen to do that.
I had a Galaxy S before and generally speaking, I actually preferred the Galaxy. The Nexus doesn't have gorilla glass, which I didn't realise before. The UI on the Galaxy looks slicker in general. The Nexus does appear to be slightly quicker (judging by frame rates in one of my own apps it's about 10% faster despite almost identical specs), although this doesn't always translate into UI responsiveness.
If the back button issue was fixed, I'd rate the two phones about on a par, but I'd think long and hard before paying extra for a Nexus.