I get bored quickly with riding around in circles.
I find that I have alot more enthusiasm for biking when there is a purpose. We do alot of local and even not so local shopping, errands and trips by bike. We also take long weekend tours, sometimes camping and sometimes lodging and sometimes mixing it up. We try to find interesting and fun destinations and routes with places to visit along the way. The planning and anticipation of a tour always gets me stoked to go. Also we like to throw the bikes in the car and head to fun places. We are on the opposite coast but exploring Washington DC and the surrounding Northern Virgina area was alot of fun on a bike. Shenandoah National Park in Virginia was a blast to bike through and hike as were the White Mountains in New Hampshire.
Also I have a carbon road bike, a touring bike for the trips and errands, a hardtail for the trails so I can grab something different, go out on club ride one day and head for a trail the next, do some grocery shopping, whatever, mix it up. Planning a new purchase this winter of a fixed gear bike. Variety is the spice of life.