This is an excellent idea. In fact, I'd love to see this expanded into a complete dataset of acquisitions with at least the following data: major subject area (e.g., email, storage, etc.), year founded, year bought, amount bought for, number of total staff after one year, revenue after one year, number of total staff at acquisition, revenue at acquisition).

This could be useful to detect broader M&A trends by subject area. (Which is one possible way to decide on a business - by likelihood of M&A exit - not necessarily a great way, but worth thinking about.)

It would nice if you could also show a chart/graph of which companies and acquisition count. So I think Yahoo is leading the way close to 5 acquisitions or so

It would be worth mentioning Opera's acquisition of FastMail, and FastMail's subsequent split from them.

Missing Mailgun & Rackspace.