My taskbar problem is similar to those described here, but I'll explain the differences and what I found is causing the problem.
The more annoying problem is that every so often, only a thin line will show up for the taskbar as if the bar had been sized to zero, except that grabbing the line and trying to drag it up to increase lines doesn't work. This effectively makes it impossible to access the taskbar or system tray in any way.
I have experienced a similar problem (taskbar going crazy, flashing of the icons at high speed, ...). I had been using Vista for 16 months and everything (almost) was perfect until two weeks later.
For the last two weeks, I have searched the Internet, hoping to find an answer that would allow me to solve my problem. At first, my most plausible hypothesis was that my computer might have had suffered from over-heating, what could be causing the whole thing. However, I ran some tests and the evidence was not pointing towards that direction.
This morning, while I was about to give up, I desperately pulled the USB cable that connected my wireless keyboard and mouse to my computer. Suddenly, everything went quiet. No more flashing of the taskbar. I was free again!
I am now 99% sure that a malfunctioning of a wireless keyboard (or mouse) is what causes the problem, at least in my case. So if you are under a similar curse and that you have been using a wireless keyboard, you might want to have a closer look at it!
As for me, I did not have the chance to buy a new keyboard yet. So when the taskbar goes flashing again, I just have to make sure that the mouse is closer to the wireless receptor than is the keyboard (note: my keyboard and mouse are governed by the same receptor). This little adjustment seems to be enough to prevent the flashing. However, I will purchase a new keyboard as soon as I get the chance. Only then will I have the right to use “100% sure” instead of “99% sure”.