the thing that bugs me about tivo the most if that if you're watching show thats not being recorded, but not live, and accidently change channel you lose it, or if you press a menu button it jumps to the end of the buffer.
mine is the iphone, takes ages to boot up, battery life is just awful, can't multitask properly ,when its checking email it lags so badly sometimes you can't answer calls, when you hold it upto your ear sometimes the buttons get pressed and it puts it in mute, or hold, sometimes ignores key input or lots of lag, poor levels of customisation, puts odd suggestions for words, keyboard doesn't always appear, for some reason switches to caps mode after i press certain letters, poor antenna, when its mute some sound still play, sms notify keeps playing if you don't read (can't seem to turn that off, i'm hoping its me and ive missed the setting)., vibrate motor is really crazy when its on a hard surface, gets really hot after long usage.
then basic stuff like call black/white listing, why can't phones have programmable silent/normal modes, ie after 12am til 9am it goes automatically silent or quieter, with whitelist support.
obviously some of them are common to all phones, no ones designed the killer phone yet, given how many of them there are its odd.