I'm a bit late in the discussion, but here's my experiences (my own schooling and DC17):
DC17 has subject accelerated in science multiple times. It was difficult to get her the acceleration she needed, and it was challenging at times with high school scheduling (some regular classes, some AP classes, and some post-AP courses) and nonaccelerating in other subjects (such as math). It's worked out well in the long-run, though. She was much happier and more confident in her abilities.
Back in the dark ages, I was accelerated multiple times in various subjects and accelerated (and un-accelerated due to district policies) with full-grade skips. When I was about 7, it was obvious that I needed something out of the ordinary, and one of my teachers allowed me to join the middle school accelerated humanitites program for a few subjects a day (5-7 grades accelerated at that point). It eventually became an independent study/private tutoring arrangement when I outran the middle school program. I very much enjoyed being in classes with older students and discussing literature, history, and philosophy with them. However, due to age differences, I wasn't able to pursue the same activities they pursued (sports, programs for middle schoolers with age restrictions...). The independent study set-up alleviated some of those issues, as I had more access to older students' activities outside rigid district policies.
As I grew older, I ended up accelerating several years in math and science, as well, through independent/partial homeschooling opportunities and early college opportunities. Those were probably the best memories I had from my childhood and teen years. I loved the intellectual stimulation and the social experiences with others sharing my interests. However, it was very difficult to arrange logistically within district policies, which arbitrarily could reverse acceleration as policies changed. I would advise going through those rules and regulations on your own before making the decision to make sure that there aren't loopholes that could create problems in the future (age minimums on starting middle school/high school, issues of credit for courses later on...).
