What do you see as the downside of tubes?

Nice thread and some very good points both pro and con. I like the sound of tube amp and the ease of a good sounding SS amp, I use both, but all of my SS amps lean toward the sound of tube amp. Since I also own the Mastersound 300B SE I am going to address your questions with this amp in mind. The Mastersound only has 6 tubes, 2 of which are the 300Bs so heat is not really much of an issue, compared to most tube amps this one runs pretty cool. My Mastersound amp is the higher output version which uses either the 32B or 300BXLS tubes and yes these tubes are quite expensive, probably around $625 for a pair of 300BXLS tubes, the 32B tubes cost much more. However, new regular 300B tubes can be found for around $150 for EH to around $350 for a pair of really nice Full Music Mesh Plates all the way up to very expensive Western Electrics with various price points all the way up. The other tubes, 5687s and 12au7s are very inexpensive, so overall tube replacement is not all that expensive or much of an issue.
Biasing the 300Bs will require a meter but those are cheap and biasing the output tubes only takes a few minutes. Once the tubes settle in I only need to check the bias about once a month and rarely do I have to make any adjustments. So overall the downside to this particular amp is very small in relation to the sound it produces.

I was a solid state amp/tube pre-amp man for years. My systems sounded great. Then I purchased Canary monoblock tube power amps and mono-block pre-amplifiers. I have not listened to my superb solid state set-up 30 minutes over the last month or so.

The sound of an all tube system is so seductive. Semi hit the nail on the head, at least for me, in his post. I don't like the maintenance but I am now convinced that the sound of tube amps make the headaches of biasing and testing tubes worth it.

Now that I have tried tubes, I will never go back.........

Seriously Unsound, what the hell have you been smoking?? And no, I DON'T want any.

I was never more seriously involved with the music and this hobby until I started acquiring tube equipment. I don't see any downside at all. I personally would never consider the cost of tubes or biasing to be a downside. It's no different than performing maintenance on your automobile. Of course, this is just my opinion!

Unless you or your pets (or both) are having sex with the the amp, I wouldn't think burns would be an issue. No more than a hot stove and usually a warning will suffice there for those that don't know better (or they'll learn fast enough). Besides, most have covers or grills.

The majority of new tube amps should be reliable, but if replacing lightbulbs in your home is too much of a headache, then a tube amp may not be the answer.

I've owned both, to me my current tube amp sounds the best of any I've owned and it does great in home theater duty too.