Yes, even I have a couple older browsers on my machine — for the simple reason some of my users still — well use them.
As for managing multiple browsers, as always WebMaster World has some useful information — while A List Apart justifiably curses such necessity. Surprisingly, it is Microsoft that offers an article on how ‘listening’ to your users User Agent can make you a better developer. Which is contrasted with the WaSP page some developers redirect users with what I like to call bowswer browsers.
Finally, here is a semi-definitive list of MSIE competitors that includes short historic describes the various browsers we as developers have to contend with.