I've been listening to random years of the show since last December. Mainly because of what I was able to download archive-wise so I can listen on my phone. I didn't discover the show until late 2012, so while keeping up with current episodes, I also listened to the older episodes as far back as iTunes would keep. At some point, I will have listened to all the episodes, but I haven't gone completely in order.
It's been really interesting to hear the show at different points and notice the shape it took since it started. Listening to the first year and half, it's amazing how quickly the show found its footing, and just constantly seemed to evolve from there. I remember Tom saying towards the end that the show became something that was unrecognizable from how it started, so I've been enjoying the parts in between.