The "Volley" rule
Page 42 of the 3.5 Rules Compendium includes the following:
A form of attack that enables an attacker to make multiple attacks during an action other than a full-round action, such as the Manyshot feat (standard action) or a quickened scorching ray (swift action), allows precision damage to be applied only to the first attack in the group.
I am of the oppinion that this rule should be either ignored or altered to address the issue it was trying to solve.
Why the rule is broken
The clear intent is to cut down on the power of Sneak Attack abuse, but the full-round action limitation is arbitrary, and the examples actually make the rule more complicated. Manyshot already can't apply precision damage (it has a "Special" block which specifically says so). The Quickened Scorching ray example makes sense, but still leaves Standard Actions unanswered. Does a regular Scorching Ray work?
How to get around it
Greater Multishot bypasses this rule because specific always trumps general, and Greater Multishot specifically says that each arrow applies precision damage.
Sorcerer/Rogues also have an easy way around this: metamagic. Because Sorcerers increase the casting time of their spells when they use metamagic, they suddenly have a whole pile of full-round actions which are allowed to apply precision damage. A Split Ray Scorching Ray fires up to 4 rays (depending on caster level), each dealing precision damage. Non-Sorcerers can use Ocular spell to get around the issue too, though not so frequently or effectively as Sorcerers.
What the rule should say
A form of attack that enables an attacker to make multiple attack rolls during an action other than a full attack action, such as the Quickened Scorching Ray (Swift Action) or the Dual Strike feat (Standard Action), allows precision damage to be applied only to the first attack in the group.
This makes it clear that if you want more than one sneak attack you need to make a full attack action. You can get one more from a swift action, but not a whole pile like you could with a Quickened Scorching Ray without this rule.