I'm with those who have more fun with fashion in the fall; second is spring. For me, fall is like fashion new year, whereas summer is, like binkle said, more like "grin and bear it." And winters for me now are about what works in rainy cold.
But I admit that I hadn't thought about when I wear more trends. I think that these days, I enjoy trends all year round. However, many of my "trends" are more to do with styling rather than buying specific items. Or, like kaelyn, I may buy a piece that happens to be trendy but I think of as having longevity *for me*. For example, I have a few bell sleeve items that are up to 15 years old because I liked the look when it trended previously, and I'll wear it regardless of whether it's hot at the moment or not.
Then there's the factor of trends acting differently from the way they used to. Some items have a very long arc of staying on trend like Angie has pointed out, but I've also noticed mini trends flickering in and out in a very fast frequency. What is new to me about that is that they come back at all after dropping out of sight, and quickly. So if something goes away, it might have a surprise comeback in the next 6 months to couple of years.