The creative zen micro can't even be compared to the iPod nano...they're in a totally different class.  Ipod nano is the only one in its class, and the zen micro is in the small HD class.  The dell pocket DJ is there as well.  The regular dell DJ is a tank...seiously.  Its freaking huge.  By volume, the new 30gb ipod (299$) is actually slighly smaller than zen micro (5gb, $179), and a little larger than the dell Pocket DJ (5gb, $179).  The regular Dell DJ (30gb, 259) is 75% bigger (by volume) than the 30gb iPod.  The dell also has LESS battery life (12hrs vs 14) than the iPod, no color screen, no video capabilities...If you are in the market for a full size, i think the iPod wins hands down.  If you're in for a smaller one, the Dell Pocket DJ is priced well. than the nano and is relatively small, but is still twice as large as a nano.
Everybody in my family has an iPod (i have two- a 40gb and a shuffle).  When i first got my hands on each one, I made sure i charged it up all the way and ran it all the way down.  I do this once a month and the battery life is still really good on all of them.  My 40gb once had a hard drive failure, and i sent it back and got a new one within a week.  Apple has really good service.