It never fails. If I forget to try to download the patch first thing in the morning, before the servers are up, or at work any time during the day, I almost always have issues downloading the patch. My "glorified dial-up" doesn't help (it's the cheaper variety of the cable modem), but for the one time every once in a while that I want to download something, I can't justify paying more. But that's not really the point. For some reason, I always seem to get stuck around 97-98% complete. Last night was no exception. It sat at 98% for about 10 minutes, while I was talking with guildies on Vent.
From what I've read on the forums though, I'm not alone. So, the tip for today is: if the downloader gets stuck and doesn't seem to be downloading anything else for you, simply close the downloader, launch WoW again, and voila! You'll download the remainder of the patch just as fast as you normally download. (And no, you don't have to download what you're already downloaded.) After the 10 minutes, I remembered this trick and the remaining 0.8 Mbs downloaded in about 10 seconds.
p.s. I'm headed to Yosemite tomorrow morning for the weekend, so I won't be posting again until Monday.