My PS3 downloads are very fast 1MB/min or more usually. (ADSL2+)
Are you using a DNS switcher to access Netflix (like www.unblock-us.com). I think PS3 is on Akamai so that could cause problems if you aren't using your ISPs DNS.
I don't know of any ISPs throttling PS3 traffic, and I don't know why they would anyway since it is not international traffic and hardly likely to make up a significant portion of total traffic even if it was.