brf is right, you might eventually have a coupling cap failure, but that's true of any tube amp and the design of the SLI-80 makes replacing the caps relatively simple and inexpensive.
I disagree with the idea that the life of tubes in an SLI-80 is short. I ran mine for many hours every day for about three years and never had a tube failure or any degradation I could hear or that showed up in testing.
At the same time I owned the SLI-80 I also had a Rogue Cronus integrated. That's a fine sounding amp from a great company but, without any actual evidence to back up the impression, it seemed as if the Cronus was harder on signal tubes than the Cary. Tubes that worked beautifully in the Cary were sometimes microphonic in the Cronus. Again, this is just an impression, no real data to back it up and my experience with service from Rogue was excellent.
I agree with truemaineiac, tubes are just very expensive light bulbs and if you're not willing to deal with fiddling with them occasionally then tube amps aren't for you.
I'm rambling on here but the SLI-80 is one of the nicest pieces of gear I've owned and I don't think you'd regret buying one.