In my last post I mentioned a webcast about honeynets and honeypots by Lance Spitzner. Last week he posted a short report titled "Know Your Enemy: Trend Analysis" which is an analysis of data collected by the Honey Net Project. (It is one answer to the question, "what does one do with a Honeypot?")
http://www.honeynet.org/papers/trends/life-linux.pdf
The report says that some unpatched Linux machines remained on the Internet uncompromised for up to three months. This is considerably longer than I would have predicted.