P&G profits are down... at least part of that is because of us, so I'm proud.
More seriously with that thought - we don't boycott them entirely (even though that's my wife's ex-employer) but ever since she got her notice almost a year ago we've generally tried to buy the alternative/generic product in any category where we'd otherwise be buying a P&G product. What's amazing is just how many product categories they are in - it's really tough to avoid their brands.
The biggest thing for us was replacing Tide, Cascade, and Bounty paper towels with the Costco-branded alternatives. Even if P&G manufactures those for Costco (which I don't believe they do), they should make less money that way. On the other hand, I'm still using Right Guard and Gillette shaving cream. One does not grow a full beard for that sort of principle!
I know better than to think that we actually make any difference at all like that. But it's the gesture more than the reality that matters sometimes. I still haven't bought a Boston Herald since they ran the picture on the cover of a dying Victoria Snelgrove in 2004. I didn't read it often and they really don't care about my avoidance, but it matters to me and that's all that counts.