Mark Bernstein in his presentation "Blogtalk" mentioned the importance of having "sunset policies on blogrolls." I'm not sure, but I believe his reasoning in part was due to preventing a few blogs from having undue influence over others. In fact, Mark in a talk in Australia states:

never put an A-list weblog on your blogroll

It also makes sense to me that if we want our networks to evolve and our learning to grow, then we need to change our networks at times to acquire new perspectives, or else our writing and thinking can become insular and self-confirming. We don't learn as much from those who think like us as from those who think differently. Of course, I don't plan to completely overhaul my network frequently. Learning needs a mix of change and stability. So, for stability, I'm thinking of keeping non-A list blogs, and for change, adding new blogs at the top (perhaps marking them "new" for two months?). Email me and let me know what you think about a changing blogroll.