vacuum output question

I have a system backed by a PostgreSQL DB at a customer site that
mysteriously slowed way down - and couldn't keep up with the load for
no apparent reason.

I had them run a vacuum analyze verbose on my database, and had these
lines come back which made me suspicious:

INFO: index "ix_cpe_ispid" now contains 41626 row versions in 13727 pages
DETAIL: 5224 index row versions were removed.
1543 index pages have been deleted, 1373 are currently reusable.
CPU 13.09s/3.51u sec elapsed 157.85 sec.

INFO: index "ix_cpe_enable" now contains 41628 row versions in 29417 pages
DETAIL: 5224 index row versions were removed.
3706 index pages have been deleted, 3291 are currently reusable.
CPU 31.27s/8.22u sec elapsed 687.60 sec.

INFO: "cpe": found 5224 removable, 41626 nonremovable row versions in
1303 pages
DETAIL: 0 dead row versions cannot be removed yet.
There were 22416 unused item pointers.
0 pages are entirely empty.
CPU 44.46s/11.82u sec elapsed 852.85 sec.

Why did those particular tables and indexes take _so_ long to vacuum?
Perhaps we have a disk level IO problem on this system?

Can someone tell me what 'CPU 44.46s/11.82u sec' means? I have a
guess, but I'm not sure.

Thanks,

Dan