Ever focused on running organically grown businesses, the 37signals team points the failure of most (or all) of Yahoo's acquisitions, and ends with the meta-point:
Is this the future fate faced by most acquired tech companies? Is the cash worth it to founders who have to watch their creations slowly decline into obsolescence? Is freedom better than building and honing a big, popular product? When a company is bought, does it deserve acquisition congratulations or condolences? These are questions we’ll be looking at more closely (and talking with founders of acquired companies about) here at Signal vs. Noise soon. Stay tuned.
It'll be interesting to read those interviews, no doubt, but make sure you also read this excellent post by Ben Horowitz on when to sell your company, if you missed it before.
37signals have their philosophy about how to do business, and it's impressive that they stick to it and keep explaining it to everyone, but advising all companies to avoid acquisitions would be a context-free over-generalisation.