So today, pretty much everyone has widescreen displays. That is, displays that are far more wide than high. This was not always so. In ye olden days, computers were mainly used for displaying text, hence displays tended to have a similar layout as books or magazines. Today, they are more like movies (which might be worrying in itself).
So todays displays are widescreen. To do all that modern stuff, like watch (widesreened) videos or multitask (display two windows side by side). However, this also means that vertical pixels are something of a scarcity. Especially on those small Laptop screens. In fact, the first Netbook screens were so tiny that many of Windows' own windows could not be used at all since the lower parts did not fit on the screen. Raise your hand if Word 2007 leaves barely ten lines of visible text between all its blue-tinted UI-splendour on your laptop screen.
This gets most straining when reading text. On the internet for example. There is practically no website at all that can be displayed in its entirity even on one of those full HD displays. Print-formatted documents are a similar matter. Actually, I find myself craving for pixels regularly. I even disable the bookmark bar in my browser to free those extra two lines of text. And I memorize keyboard shortcuts so I can hide toolbars. And I use Google Chrome instead of Firefox/Safari/Internet Explorer, not least of all since it has the smallest title bar and no bottom bar.
Why, then, do modern operating systems still waste so much vertical space with that Dock/Taskbar? This is something I really don't get. Vertical space is such a scarcity, yet virtually every operating system choses to waste at least three lines of text with something that could easily go on the side of the display. Well, at least on Windows 7 and OSX that is something you can easily change.
So if you are like me and appreciate every added line of text, do yourself a favour and put your Dock/Taskbar on the side. Really, this should be the default.