Depends on the style, I mix tech house/minimal generally and sometimes long 2-3 minute mixes are perfect, I'm from a more "traditional" background and was brought up with long outro-intro mixing. I generally don't like when a DJ is cutting, doing short mixes, throwing effects all over the top of a tune, tends to piss me off in 99% of the cases (James Zabiela is a perfect example, technically brilliant, but annoying as hell to watch) Look at DJs like Digweed, Burridge, Villalobos, Derrick May etc etc you never hear them mashing tunes up, it's just a different style. not right or wrong. Certainly not a sign of a bad/boring DJ. It's gotta be done right though, on the 32/64 bar, in key etc etc.