I've put modern stuff through a pretty wide range of conditions, for long periods of time, repeatedly. No significant problems to report up until the point that it gets stupid, like slush freezing things into solid bricks. Most of my mtb experience is with sram drivetrains, although the 105 on my commuter has held up commendably; the cassette, chainrings and derailleur pulleys just reached the end of their life after nearly three full years of 4 season commuting and after they were replaced the whole drivetrain works like new again.
In my opinion the last few generations of stuff is pretty darn reliable.