Hmm, always a good one for discussion, as a general rule I use minimum 1x Memory, pref. 1.5x mem. However, as above there are exceptions if there is a lot of mem installed.
We don't install apps on the root disk, they go vg01 etc...
Systems now come with 72GB internal disks so after the O/s is on there is often plenty of space for a generous amount of swap.
There is also the discussion about secondary swap.
I'm lucky, I work for a very big company so the cost of a extra few GB of disk is not an issue.
I'm sure we are generous in some cases, but we don't get many issues re. swap space.
Interesting one about Sun and 30%, a Sun instructor once told me that a Sun box should have enough mem. so it doesn't swap !!! Hmm, good sales pitch, but the recommendation of 30% seems to confirm that.
Martin