If you are experiencing OTA problems with the ICS update, I suggest you try doing it with a computer. You first need Samsung’s desktop companion, Kies, which you can download here for your Mac or Windows desktop computer.
I was really quite frustrated when Samsung pushed the OTA update as the server connection was not consistent. Trusted that millions of others were doing the same update, there was no way to bypass the server but I did find the desktop update much easier to deal with.
But a word of warning. Kies for Windows is very buggy. My brother tried to update it via his Samsung Netbook and it failed to do so, citing some Windows errors that was incomprehensible at best. Kies for OSX Snow Leopard is much better but is really slow, probably due to the overloaded servers. The 300MB+ file took under 3 hours to update to the phone.
Upon first reboot, your apps will run slow. This is for the system to optimize and I suggest you do a second reboot for it to run smoother.
And yes, there are still some old apps which are incompatible to ICS. You have to weed them out as you go along. I found GetGlue to be one of those.
Though it runs far smoother and has nicer transitions, ICS has not saved me on battery life. It still runs the same as Gingerbread. Most of the bugs in Gingerbread has not turned up. One annoying one is upon reboot, where a ring tune gets played over and over. The only way to shut it is to turn on and off the notifications.
So far, I am still testing ICS for durability so stay tuned.