I think it depends on your goals. I have a somewhat lengthy list of companies whose products/services I will not buy for various reasons. I don't consider it a "boycott", though, because my intent isn't to encourage those companies to change. I simply don't want to support them. Doing that works very well for me, because my entire goal is to avoid involving myself with them.
I combine this with another "vote with my dollar" practice -- with everything I buy, I buy as local as possible. Ideally, this is a small businessperson in my community. I do this because I strongly believe that I could not have achieved the success that I have achieved without the active support and investment of my local community -- so staying local when possible is one way I can repay my neighbors for that. That works, too.
If your goal is to change the behavior of large corporations, then yes -- not buying their stuff isn't going to accomplish that unless you can convince a really large number of people to join you. That's a real boycott, and history shows us that its effectiveness is spotty.
