I have absolutely no WiFi issues, WiFi functionality has been improved hugely compared to 2.3.6!
In 2.3.6 I had a lot of problems with WiFi in which it "looses" the connection but the icon stays green. I had to disable and enable WiFi to get it to work again. This was a basic Gingerbread problem since the Galaxy Gio that my wife uses has the exact problems as well.
As for the other problems mentioned here, charging takes no longer then with 2.3.6 and I really love the new UI. It takes a little getting used to but since I allready have a Honeycomb tablet it is very easy to get to grips with.
The new search bar is great in my opninion, for a Nexus S you could do without since you allready have a search button but I like it anyway.
The phone is now way more responsive and faster, it really feels like a new phone.
The boot time is not that much slower compared to stock 2.3.6 so that is not a problem for me and anyway how often do you reboot your phone? For me it is about once or twice a week or when I need to turn it off. I allso have a Blackberry Torch, that takes more then two minutes to boot!
One thing that I have noticed is that the first boot after flashing takes a long time and the subsequent "application optimisation" as well. I didn't find the phone to be very responsive when it was ready. I did another reboot and it was much quicker that time!