What do you see as the downside of tubes?

I have decided on getting a tube amp and it will be the integrated Mastersound 300B driving a pair of Living Voice Avatars, so at least that decision has been taken.

My main question is what you see as downsides of having a tube amp. As I've decided on getting an integrated tube it's really about what the downsides are I might want to know about beforehand.

The ones I'm aware are the following.

-The tubes need to be replaced and in the case of a 300B this will be somewhat costly.

-Bias is another issue but I'm not sure how big an issue. Do you plug in your meter every so often or just when you roll tubes or replace a dead one? The meter as such isn't gonna be a big issue as I don't think it's that expensive.

-Heat won't be a big issue as we have no kids nor a nosy dog that could get burned. Hope my electricity bill isn't gonna go through the roof, but then again, I can't quite imagine that.

I'd appreciate if you could add whatever your experiences are regarding this question are as I'd like to know more before I buy it.

If the amp has a standby selector/switch then 24/7 should not be a problem;I think it is more a personal choice.
I don't leave mine on 24/7 and they have a standby switch;I know inrush current flow and tube powering on and off can be a cause of early tube failure but I think it is more a design issue;if implemented well it should not be a issue.
I sure wouldn't mind if Ralph from Atmasphere stuck his head in on the 24/7 aspect just to hear a designer/manufacturers point of view.
Not good to run tube amps 24 hours. Unless you like replacing tubes. Most all tube amp warm up fast. Uli Many of these posts refer to large power tube amps these run very hot the se300b a SET amp does not it will not heat up room will not require extra AC.
I'm not really worried about the heat or power consumption anyway. The Electrocompaniets got warm but not too warm and I don't think the 300B's will be worse.

Maybe I give of some heat due to audio excitement but that's probably gonna be it.

Still surprised for how long this post has been going :)
Unsound must have been involved in an abusive tube amp relationship in his past.

The downsides can be dealt with. As is easy to see, many of us have determined that those hassles are easily worth bearing for the sake of the sound quality. Although there are excellent SS amps to be had, it really seems that tubes with good compatible speakers is the place to be.
I am not sure that Unsound is completely off. We all know that speaker/amp match is important. But can you find a set of speakers that meet the following:

1. flat impedance curve
2. larger woofers (> 11")
3. no built-in amps
4. plays down to 30Hz (-3dB)