My Mini has been a workhorse for me. I have the late 2005 edition with the 1.5 GHz G4. I am in graduate school for history, and I use it to write all my papers and put together Power Point presentations. It is also great for chat and web surfing, though YouTube is slow these days.
So, to answer your question, the Mac Mini has been historically reliable, and it ages well.
So, to answer your question, the Mac Mini has been historically reliable, and it ages well.