Any out there who fly just for fun?
Yep. Started learing to fly in 1999, got PPL 2001, PIFR 2009. I do about 50 hours a year,
Cost share with mates from work?
Plan random trips with or without holidays included?
A trip a year of three to four days duration, cost share with mates, have done trips of up to two weeks across Oz. Four or five AngelFlights a year (they provide fuel). Occasional joy flights, sometimes solo, to maintain currency.
all GA, mainly C172/182, no ultralights.
Do you own your own plane/ share in a plane/ or just hire from a school.
More economic to rent in my opinion, also any maintenance surprises become someone else's problem.
Help aviation related youth organisations occasionally, volunteer for a week at Avalon airshow every two years (you don't have to be a pilot to do these).