Sun makes plenty of acquisitions (mostly startups):
1) Hardware
2) Giant
3) Enterprisey
None of which are very applicable to the original question, which is about web software startups.
You must have read a different question than I did. The original post mentions "startups", not "web software startups". Many News.YC readers are building things that Sun would find interesting, so I think Sun's acquisition history is relevant to our interests here at News.YC.
DTrace continues to blow my mind.