I'm still using the original Clip I got back in 2008. It's not supported by Rockbox, but I'm perfectly happy with the last official firmware. The OLED has deteriorated, but it's still fine indoors (it was almost impossible to read outdoors from the get-go).
The battery lasted around 14 hours when it was new, now I'm getting roughly half of that. I seem to remember someone on the now defunct anythingbutipod.com replacing the battery, although they had to break the player apart to get inside.
Even the damn plastic clip on the back still works!
They must've made the headphone jacks sturdier on the original model. Both the Zip and Plus had the same loose jack issue for me after a while.
On my third one now which is beginning to show the same issues but the prices have gone up to the point I'll try and repair the jack on an old one instead of buy a new one. Doesn't look too hard beyond the prising open part, which from what I gather is a bit tricky given the size and how well bound it is
Battery has basically never died on me, the amount of charge it gets whenever I remember to connect it to add some new podcasts seems to just make it last forever.
I also have a very fuzzy recollection that the batteries weren't especially replaceable, meaning we've got a finite time before they're all bricks...