Reading Vijay Pande's blog, he's told us that they've reset server 171.64.65.83 and that seems to have fixed the PS3 downloading troubles we've been having. I dare say this particular server didn't boot up properly after the scheduled server outage they had a few days ago. There looks to be another scheduled server outage for 171.64.65.XX network on November 5, 7 AM to 8:30 AM PST (2 AM to 3:30 AM, November 6 for us on AEDT) so if ya have some issues then, hopefully it will pass quickly.
PST = Pacific Standard Time = GMT-8
AEDT = Australian Eastern Daylight Time = GMT+11
EDIT: Seemed to be a 3-4 hour period after my two 7hr work units finished where they wouldn't then download another new work unit! However i've turned them back on yet again to download new work units. I seriously hope these troubles are behind us now for the PS3! Haha