Here is the most recent Supreme Court case on IAC claims and evaluation of them. Knowles v. Mirazanyance, ___ U.S. ___ (March 24, 2009).
In this case the appellant sought to convince the courts that his counsel's failure to advance a defense was ineffective. The issue revolves around the existence or potential existence of a requirement to advance every available defense or theory regardless of counsel's evaluation of the benefit or value of doing so. To some extent the issue relates to the client who says "do this" and the counsel who says "no that won't work," or something similar. Or to put it another way, when should appellate courts substitute the judgment of the client over that of the counsel when there are decisions to be made on how to proceed at trial.
The law does not require counsel to raise every available nonfrivolous defense.