Just got the distribution upgrade notice in Update Manager today. All download files are available now. I usually download one of the installation CDs or DVDs instead of upgrading online.
I use this mirror: http://mirror.mcs.anl.gov/pub/ubuntu-iso/CDs-Ubuntu/precise/ (Argonne National Laboratory, Chicago, IL)
I managed to get the whole 64-bit trial version CD before I could finish pulling together this announcement, getting about 90% my full capability, up to 1.3 MB/sec over 12 mb/sec vdsl.
Don't forget to use bit torrent if your subscription's monthly data quota isn't capped. i.e., AT&T Uverse and AT&T DSL.
Download also available , probably really slow for now (if a connection can even be made), at: http://cdimage.ubuntu.com/
Main web site provides download links to many more download options http://www.ubuntu.com/