Personal experience with coding standards
I've been a committer with the FreeBSD project since this summer, and I've definitely learned a lot. One of the first things I learned was that style(9) is _very_ important. Even if it takes time even to get things to where they should be -- KNF (Kernel Normal Form reference (http://www.FreeBSD.org/cgi/man.cgi?query=style&sektion=9&apropos=0&manpath=FreeBSD+4.0-current)).
Styling guidelines are really a wonderful thing. Sure, you may have a personal style to unlearn, but you save even more time after using the standard style than it took to learn it. People make mistakes with the style sometimes, but even with style bugs, things are much more readable than could be remotely possible without a standardized style.
If I'm going through the kernel, reading code and vgrepping for what I need, it takes much more effort to adjust to different styles than it does if everything is one comfortable style, and it all fits together. The biggest visual criteria covered by the style are indentation and comments. There are rules for whitespace, and rules for how comments work. In addition, tabstops are defined to look like 8 spaces, and lines are to be broken at 80 columns. Some of the more unwritten rules are ones of naming. Typically, something can be all capitals, all lowercase, and may have underscores or numbers with either one. Functions are usually all lowercase, as are variables, but exceptions that don't affect the namespace (i.e. giving your variables names you like better is usually just fine, but changing your function to something like FooBar from foo_bar is not) are okay.
Perhaps I'm a little biased by actually having to work with them, but I think that by using a good (well-defined) coding style, everyone's time can be saved, and software tends to fit together much more nicely than without a style.