The brokenness of the Dweomerkeeper is mostly in its revised form, which you can find in the web-enhancement for the Complete Divine.
More precisely, it is this ability:
Supernatural Spell (Su): At 4th level, the dweomerkeeper is so attuned to the fabric of magic that she can manifest spell effects with almost no effort whatsoever. Once per day as a standard action, she can use any one spell with a casting time of up to 1 standard action as a supernatural ability. The spell chosen must be one that is currently available to the dweomerkeeper (that is, one that she has prepared or that she knows and has a spell slot of the appropriate level available to cast), but she can decide at the moment of casting to use this ability. The spell functions as it normally would and is expended normally, but the dweomerkeeper does not require any components, does not provoke attacks of opportunity, and ignores the target’s spell resistance, just as if she were using a supernatural ability instead of a spell. At every even-numbered level after the 4th, the dweomerkeeper gains one additional use of this ability per day.
This means you can cast
wish or other spells with XP components without losing any XP, or cast
true resurrection or other spells with very expensive material components or focus without sacrificing your wealth.
Hence all the claims of brokenness.
It is true that, IMNSHO, casting four wishes a day without losing XP is somewhat off-putting for the average DM.
(And yes, you can have level 9 spells. Prerequisites are easily met by a cleric 1/wizard X or cleric X/wizard 1, so you can end up, spellcasting-wise, as a cleric 19/wizard 1 or as a cleric 1/wizard 19.)
Mind you, the prospect of potentially being able to cast all five
wishes required to give you a +5 inherent boost to one ability by just spending 5000 XP is enticing.
