When I first got the iPod I started to use it with this plugin.
My main reasons were:
1. I was already using winamp.
2. The winamp media library makes it easy to add newly added songs to my Music Folder (whereas iTunes will make doubles if you press "Add Folder" after adding one or two songs).
3. Winamp automatically updated the library when I deleted files with Explorer (iTunes leaves redundant listings that you dont realise are missing until you try to play them).
My general experience was good. It wasnt as intuitive as iTunes but once you figured out where all the buttons were, transfers went fine for the most part...
I did try including a playlist though: static ones were ok, but when I tried to add a smart playlist it deleted all of my playlists instead. After that, on the next transfer, it deleted half my songs before putting the new ones up and it generally became to erratic. Maybe it has been fixed by now.
Now I use iTunes. I take care to add only new songs and delete songs from both the iTunes library and explorer when organising my music and it is working fine. Winamp does have its positives, but iTunes is ultimately a better, more reliable way of using your iPod.
One thing: Winamp would always leave one song of the iPod. If there were 2000 songs in my library only 1999 would transfer. I have no idea why. iTunes did this too until recently, and, I dont know what changed, it not updates all of my songs. Weird.