I love my Sidekick II. I would never ever change my phone ever again until the Sidekick III. The AIM/Yahoo feature is nice as well as e-mail along with the addition of 3 POP e-mail accounts you can add. Now I can e-mail/IM the husband mini grocery lists before he gets home from work!
And the camera phone is great for those candid moments.....the games are a nice added feature as well. The most widely used feature that I use though has to be the calendar. I have it set to when all my meals are going to be, appointments, etc.. It alerts me at the time I set it at or 1-30 minutes beforehand if I want. Pretty cool.