At home I personally use a 2.3 GHz dual core Powermac G5 about 2x a week. It was used more often as a video server for my home system, but PMS stopped supporting these models so that task went to my hackintosh. I still use this beast for editing student films for work (I still prefer the old version of iMovie), capturing streaming audio, and creating DVDs.
At work I brought in my brother's Gigabit Ethernet G4 (upgraded with a Sonnet 1.8 GHz G4 and 1.5 GB RAM). My students use it: to play Classic educational games, for word processing, to create Powerpoint presentations, for storing and editing photos, to create iMovie projects and to play music.
However my oldest in my collection is my Mac IIsi. It still freakin' works running OS 7.1. I still have 3.5" disks with games such as Shadowkeep, apps like Lotus 1-2-3, MS Word 4.0, and Hypercard. I turn it on and use it whenever I get nostalgic.