Out of curiosity, why 2 taskbars?
I am guessing you have never used Ubuntu (or a similar distro) before. Ubuntu comes standard with two taskbars (one on the top, one on the bottom of the screen), once you get use to it, it's really productive. I'm a huge Linux fan and I've always found being able to have as many taskbars as you want to be a very useful feature.
Windows 7 has drawn me back to Windows. For over a decade I have wanted to add a second taskbar in Windows. I like to organize things in a way that is convenient to me, and that's particularly true when it comes to computing. As for having two taskbars, if you look at it logically, it makes sense.
My screen is 16:9 (1366x768) - obviously I want to maximize vertical viewing space for websites (and etc). So having the taskbar on the side of the screen is a given. I often run a lot of applications at once - I want them all to fit on my taskbar. Resizing the taskbar while it's on the side of the screen does NOT add another row ((technically) column). Resized: http://img145.images...04/donationcoder.png
Small icons look bad (shadows are crooked). While the taskbar is on the side of the screen, using small icons does not make the taskbar any smaller. Small icons make the taskbar look bulky (for lack of a better word to describe it), not to mention they're kind of small for viewing on my 15' laptop screen. Basically I just want to maximize the room for running and pinned applications while still having quicklaunch icons and everything else. I actually got rid of the start menu button since it's useless to me as I always open the start menu with the windows key.
Those are the reasons off the top of my head, I'm sure I could think of more if I tried.