I've run Linux boxes with LVM for around 9 months now, without any hiccups.
It's been in the Kernel since 2.3.x, so, most of the bugs seem to have been shaken out (and, I've never seen any).
I've run Oracle ontop of LVM, without any hassles, so I can't see any difficulties running oACS/Postgres ontop.
It's _extremely_ useful, I gave a talk to the Scottish Linux User Group last month, on enterprise Linux servres, the slides from that are available at http://www.tech-linux.org/enterprise/.
Yes, go for LVM, although you won't survive without it, once you've used it :)
Kevin
