One of the things that make it most frustrating to use the web from an iPhone is form inputs. Reading the content is generally doable - and if not, there's always Instapaper. But form inputs are always a pain. Partly this is because they're over-styled, so you get stuck with fields that are either tiny or huge. Sure, testing that sort of stuff gets annoying fast. What about the stuff that is easy to do right, though?
One of the things the iPhone does is to show the user a different keyboard depending on the context. If the entry point is in an email address, the keyboard shows characters that are used in email addresses - the @ mark, dashes and underscores, and so on - instead of the space. If it's a phone number, you get a numeric keypad. This makes life much easier.
All of this is driven by the type of the HTML
input element. Set it to
tel or whatever, and let iOS do its thing. But no, nobody bothers to set their input element type, so iPhone users are switching back and forth, hunting and pecking, and all the time hating web developers so very, very much.
And that's just one tip for this useful list of
8 HTML Elements You’re Not Using (and Should Be). Go, and do ye likewise.