G5 is my main 'home' computer, use it for Photo catalogue and minor edits (iPhoto, Picasa and Flickr uploading etc) iMovie to create holiday movies etc. games occasionally (Doom3, Amnesia, Quake3&4, UT2004 etc) browsing, email of course, iTunes and Spotify through my Bowers & Wilkins MM1 speakers (awesome!), utility wise Dropbox, Logmein (to give me Back to My Mac functionality), AV supplied by VirusBarrier X6, Skype gets used a lot for video calls home (I live/work abroad) etc etc. Hardware attached is a Logitech HD Webcam, Elgato Turbo.264 USB encoder, B&M Speakers, D-Link USB Wifi dongle.
My MacBook is connected to my TV permanently, I use Mobile Mouse Server to control it from my iPad - It runs BBC iPlayer (through a UK VPN) and PS3 MediaServer to serve content from my Airport USB attached hard drive to my PS3 and runs 24/7 (to enable it to keep my iPlayer programs up to date and downloaded).
My MacBookPro is my work laptop - it's lovely and it's smooth but I just like using a desktop at home and the G5 is still very much 'fit for purpose'.
Have an iPad for iPad stuff..... 🙄
Use a Nokia N9 for my phone.
Keep contacts, calendars etc synced between ALL my machines (G5 on Leopard, MacBook of Lion, MBP on ML, iPad on iOS AND Nokia (!) using Fruux.