You're right, if you want to go to that extent you'd have to do a bit of research.
Myself, I've been on a sort of boycott Nestle mission ever since I was at university, with occasional relapses along the way. It is still easy enough most of the time to say no if it's got their own label on it and that alone makes a little bit of a difference. I'm not one to say that we should truly boycott everything they're involved in, just because I know that they've got their fingers in so many pies that it's nigh on impossible, unless you've got an exhaustive list of all their interests.
ps: I thought this story seemed familiar, Goz did you read the date of that Guardian article?
I think the most important thing to do is make sure you boycott things with Nestle labels on them - if enough people keep doing that then at least they'll get the mesage that their methods are unpopular. Of course it wont really hurt them financially, but it's a bit difficult (IMHO) to remember everything that's owned by Nestle.
Its a right pain how things change - a few years ago if you bought a Kitkat - you were giving money to Rowntrees who were quite an ethical company - but now you're giving cash to Nestle - who are obviously c*nts....