(3.5) Need a quick power level check on "Imbue Familiar with Spell ability"

[DracoDei]

How good is Imbue Familiar with Spell Ability, and why?
I ask because I am planning on turning it into a warlock invocation for a PrC that is focused on using the familiar in an INDIRECTLY offensive way.

EDIT: Complete Arcane, page 112 (might be other places too).

[Glimbur]

In combat, it is hideously useful. The only thing better than spells is more spells, and this lets you double your spells/round.

Out of combat it is modestly useful. Your familiar could be a bird or a rat or something but by the time you can cast 6th level spells your familiar doesn't have any movement modes you don't. It could be nice if you need to split the party or a rat would blend in better or other special cases.

[Private-Prinny]

Keep in mind, however, that wizard spells are a far cry more powerful than warlock invocations. Spending an invocations known slot on this shouldn't cause many issues.

[DracoDei]

Thank you both for your help, the first draft of the fruits of my labors may be found HERE (http://www.giantitp.com/forums/showthread.php?p=11168393#post11168393).