Yahoo! Photos is magnitudes larger than Flickr, so why would Yahoo! buy them? Del.icio.us is surprisingly small compared to the mindshare too.
Does Yahoo! see growth? I don’t think that they really care.
Both can give them a lot to learn about the web, which can help the search business get more relevant. A holy grail of search is to allow me to get results about Apache Ant vs. the insects when I search for “ant”. Contextual search. Some talk to the semantic web as a solution.
What Yahoo! now has with their properties are dedicated users who are doing the semantic tagging for them. The community is doing the work, and humans and the wisdom of crowds are better at it than the best AI right now.
A danger is that the del.icio.us user base is probably skewed to a particular set of stereotypes (tech savvy etc), but that may not matter much for them right now.
Yahoo! got communities for pretty cheap, and they don’t even need them to grow to be useful.
