Maximum Filename Lengths
One of the benefits that Mac OS X brought to the Mac-using world was longer filenames. In the old Mac OS, 31 characters were all you had to work with; you didn't have to worry about extensions, but 31 was still too short, for instance, for naming an MP3 file according to its title, artist, and album. MS-DOS, if your memory is that long, was even worse: eight characters, all in caps, and a three-letter extension. How did we ever survive?
But now we have a full 255 characters to devote to any filename, and that includes spaces, quotes, apostrophes, and all kinds of other characters (with a few exceptions, as you'll see shortly). I don't care how long the title of your favorite MP3 is; you're not going to run out of letters to describe it in Mac OS X.
One thing to watch out for, though, is that when filenames get too long to be displayed comfortably, they start to wreak havoc on the mechanisms used to display them, both in the graphical and command-line levels. The Finder will shorten a displayed filename to a reasonable length and stick an ellipsis (...) in the middle to show you that there's more to the filename than what you see. But the Unix shell is less sophisticated and will dutifully print out the whole massive filename, even if it wraps four times in your 80-column-wide display and wrecks the format of your file listing. To keep your own sanity, to say nothing of good desktop hygiene, you should probably keep your filenames to around 30–40 characters at most. But that's just some motherly advice, not a requirement of the system.