vacuum and 24/7 uptime

Is Postgresql ready for 24/7 uptime?  Our tests have shown that vacuumdb
requires downtime, and if one does this nightly as suggested, well, one has
downtime, 40+ minutes in our case.

My company wants to replace MS SQL Server with PostgreSQL, but we can't
afford downtime to do database maintenance.  Is it possible that we are doing
something wrong?

What are the plans for future versions of pgsql?  Will vacuum be optomized or
otherwise enhanced to execute more quickly and/or not lock tables?

Thanks,

Mark

PS
I posted more details to the hackers list.