The above posters have had much better experiences than many of their tube power amp compatriots. Some tube amps are guaranteed to burn your fingers due to poor positioning of bias pots and will go out of bias like changes in the weather. Not all, mind you, but enough of them.
I also respectfully submit that there are not all that many tube amps which autobias. Many of VAC's amps do (my VAC Renaissance 140's do) and the Audio Valve amps do, both of which are exceedingly fine amps. As for manual bias amps, many are indeed well designed and rarely need adjustment (but not enough of them). One example at the outer limits of luck involved a friend with Sonic Frontiers Power 3's that never went out of bias and never blew output tubes, despite being run hard all of the time.
My experience is that an auto shut-down feature to stop failing output tubes is the most valuable feature for tube amps (this is another feature of my VAC tube amps). I would not leave a tube amp unattended unless it comes from a top-notch manufacturer and has a tube shut-down feature, as some output tubes can arc or explode (a few even Roman candle!) when they fail, and many, many tube amps use burn-up resistors to protect the output transformers that can literally flame out when output tubes go (not only is it a potential fire hazard, but it requires that new resistors be soldered in).
You also need to remember that you can't just sit down and listen to tunes whenever you want with a tube amp, as they need to warm up for at least fifteen minutes or so before listening, and you really don't want to be turning them on and off four times a day, as the resultant thermal cycles are destructive. High-end solid-state amps are left on 24/7 and you can catch a listen whenever.
Good tube amps are also relatively expensive, as they require high-quality output transformers and power supplies, which are VERY expensive and result in a very heavy amp (like $10K+ per amp retail price and 100 lbs+ weight). There are simply no shortcuts to a good tube amp (if it's inexpensive and you can pick it up by yourself, put it back down and keep walking), whereas good solid-state amps are cheaper to make.
Enough negatives -- one big advantage to tube amps (besides superior sound from the good ones) is that you basically have a brand-new amp after you re-tube them. Some of the better solid-state amps become unfixable because they use limited production output transistors that go out of production, rendering the amp worthless if output devices fail. Also, when a solid-state amp breaks, you can't just pop a new tube in and go back to listening -- it has to be serviced.
In any event, tube amps certainly have plusses, but they have minuses as well and are generally not hassle-free. For me, they are worth it, but lots of people just give up on them.
