Leaving Palm Pre Plus despite really loving webOS. Given the same hardware (to be rectified soon, I know) and same apps, I might still go webOS over iOS despite two Macs in the house. I can simply navigate the Pre much faster despite using my glorified iPod Touch (a 3GS 16gb) for basically everything except calling and texting (though I use Skype quite a bit on the 3GS, too).
As a musician, I just love Smule's offerings and Amplitube, TabToolKit, etc. The construction calculators are also the best. The games! And as a supporter of good support, I like Apple's update process and timeline (i'm weird, I know). With webOS and Android, there's always so much chatter about what's coming and possibly when, then it hits different phones and carriers at different times. Apple generally means what it says, and that matters.
So I wish the best to HP/Palm and webOS and could even be swayed back in a couple years if they prove worthy. But I suspect it's iOS from here on out for me. iPhone 4 32gb for me and the 5 in June if available on Verizon.