These are just small things, but I noticed that the radio_button really sucks when using with a fields_for or form_for block. First, it ignores the :index option passed into the parent fields_for when generating its ID! Second, you cannot use f.label to target it. I fixed both of these:
http://rails.lighthouseapp.com/projects/8994/tickets/1993-fradio_button-ignores-parent-fields_fors-index-option http://rails.lighthouseapp.com/projects/8994/tickets/1992-flabel-should-work-for-targeting-fradio_button
The first one seems pretty important, now that people are doing more and more nested assignments (you can imagine someone will try a radio button sometime, like I did). All of these can be resolved by manually generating the ID of radio buttons and labels, but then why use form_for at all...