[ubuntu] Installing Ubuntu on UEFI, and GPT enabled ultrabook

I have two specific questions regarding installing Ubuntu on UEFI and GPT enabled ultrabook.

1) When installing Ubuntu, should we explicitly choose "device for boot loader installation" as /dev/sda or /dev/sda3 (EFI partition)?

2) How would I uninstall or install another distro on the same partition. Previously, we just used to reformat it. Now because the keys are stored in EFI partition, how do we remove them.

Thanks and regards