For anyone with a Mac Pro, I urge you not to update yet and take a look at this thread first: WARNING 10.7.5 just destroyed my Mac Pro
No problems on my 08, download took 10 minutes, updates was smooth and fine. Have you just held the power button and turned the machine and left it for 5 minutes? Then turn the machine back on. Large updates can often cause a few machines to hang when restarting for the first time, very similar to what used to happen with a firmware update. A simple power cycle through the system can sort things out.
I can't believe some of the responses in that thread. It hung so they tried to re-install the whole OS. I hope that person tried all the other simple stuff first.