I got ~10% hardware errors and ~10% lower hashrate mining at Eligius overnight, and switched to Btcguild this morning and the problems went away (my hashrate for November Jupiters went up by ~10% and the hardware errors went away at Btcguild).
October Jupiters using the .99 firmware don't appear to be impacted, but some November Jupiters running the .99e most definitely are.
I prefer to mine at Eligius versus Btcguild to support pool decentralization, but won't do so if it means a 10% hashrate hit.
I am not the only person having this issue. Check out the Eligius thread for more examples.
https://bitcointalk.org/index.php?topic=23768.2980I suspect it had more to do with the restart of the KNC miner than anything else.