Vacuum and Memory Loss

Hello friends,

I am responsible for maintaining a high volume website using postgresql
8.1.4. Given the amount of reads and writes, I vacuum full the server a
few times a week around 1, 2 AM shutting down the site for a few
minutes. The next day morning around 10 - 11 AM the server slows down
to death. It used to be that the error 'Too many clients' would be
recorded, until I increased the number of clients it can handle, and
now it simply slows down to death having lots and lots of postmaster
processes running:

Tasks: 665 total, 10 running, 655 sleeping, 0 stopped, 0 zombie
Cpu(s): 14.9% us, 16.7% sy, 0.0% ni, 0.0% id, 68.4% wa, 0.0% hi,
0.0% si
Mem: 2074932k total, 2051572k used, 23360k free, 2736k
buffers
Swap: 2096440k total, 1844448k used, 251992k free, 102968k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
6420 postgres 15 0 26912 11m 10m R 3.6 0.6 0:00.11 postmaster
6565 postgres 16 0 26912 11m 10m S 3.6 0.6 0:00.12 postmaster
6707 postgres 15 0 26912 11m 10m S 3.3 0.6 0:00.10 postmaster
6715 postgres 15 0 26912 11m 10m S 3.3 0.6 0:00.11 postmaster
6765 postgres 15 0 26912 11m 10m S 3.3 0.6 0:00.11 postmaster
6147 postgres 15 0 26912 11m 10m R 3.0 0.6 0:00.15 postmaster
6311 postgres 15 0 26904 11m 10m R 3.0 0.6 0:00.10 postmaster
6551 postgres 15 0 26912 11m 10m R 3.0 0.6 0:00.09 postmaster
6803 postgres 16 0 26912 11m 10m R 3.0 0.6 0:00.09 postmaster
6255 postgres 15 0 26904 11m 10m R 2.6 0.6 0:00.14 postmaster
6357 postgres 15 0 26912 11m 10m R 2.6 0.6 0:00.11 postmaster
6455 postgres 15 0 26912 11m 10m S 2.6 0.6 0:00.10 postmaster
6457 postgres 15 0 26912 11m 10m S 2.6 0.6 0:00.11 postmaster
6276 postgres 15 0 26912 11m 10m S 2.3 0.6 0:00.10 postmaster
6475 postgres 15 0 26912 11m 10m R 2.3 0.6 0:00.11 postmaster
6868 postgres 15 0 26912 11m 10m S 2.3 0.6 0:00.07 postmaster
6891 postgres 15 0 26912 11m 10m S 1.3 0.6 0:00.19 postmaster

Thanks for your help in advance,
Mike