I'm a big fan of Nike+. I'd do a post on how great it is, but it's been done before (like here -> http://www.cabel.name/2006/08/multiplayer-game-of-year.html). Many times over. For Christmas I got a pair of Puma Faas 300's, which are great lightweight running shoes. Sadly since they are not made by Nike they do not have the special compartment for the Nike+ sensor. For about a month I was able to make due by strategically placing the sensor under my laces, until one day at the beginning of my run it fell out. I went looking for it, but it was gone. I picked up a new one from a running store near my house and an Amphipod Micro Pocket to keep this one safe. Linking it back to my iPod was easy, sadly it took me some time to figure out how to get it to resync with the Nike+ website. It seems that you have to "approve" each new sensor to post to the website. Makes me wonder if multiple sensors can publish to the site at the same time, but that's another story. Anyway here are some links I used to get my sensor resyncing to the Nike+ website.
Follow these directions to get your iPod syncing again.
Follow these to get your workouts missed workouts pushed to the Nike+ site.