We developed our basement a few years ago and it was actually an enjoyable project. We left the template as it was from the builder without any major changes to mechanical room or bathroom (not shown). We tiled the bathroom and put in a shower. Also around the corner is a little office area with Avatar.
We installed a wet bar and a kegerator so we have draft beer on tap. There is a local brewery not far from my office so I am able to pick up various kegs on a days notice. Really nice for parties with beer just flowing. Hardwood in the bar area, carpet throughout the rest. There is Dri-cor throughout the basement which raises the floor a bit but keeps it a tad warmer and also safe from moisture. I had a water tank blow in the mechanical room and it would have been a disaster if not for the dri-cor.
Have a little poker table which has seen a few good nights (and a few bad!). The cabinet was custom built in with my electronics down below such as receiver, xbox etc. Cat 5 was run throughout the basement and speaker wires also run. I think most basements now have a home theatre setup of some sort. We went a 106" screen, totem sttaf speakers in a 5.1 setup with a velodyne optimum 12" sub - very nice.
The side wall is home to the pins. I never thought I'd have more than 4... now 6 and I've had to shuffle Avatar into the end office. I had to part with ToM to make room for Star Wars. Stand up arcade in the back is Bubble Bobble - all time favourite. (Not an emulator).
Total finished space added about 900 square feet. I don't think I have any regrets with the design (going on 5 years now) except for more space in general would have been nice Oh, exercise bike was an after thought but needed due to having beer on tap in your house. haha.