I've been running a 1x9 set-up on my 'winter' mountain bike for the past couple of years.
An 11-34t cassette and a 34t stainless steel Surly chainring with a chainguide.
Despite living in the Peak District and regularly tackling 1 in 4 climbs I have rarely missed the lower gears. Granted I have got alot stronger and adapted quickly to this set-up.
I took another bike out recently which had a 3x9 set-up and found the steeper climbs more tiring when spinning up in the granny ring.
Something to do with the slower speed/longer duration and the increased leg movement I reckon.
Anyway, apart from increasing fitness, I have found the 1x9 set-up much quieter, lighter and more reliable than a triple up front. It's also quicker and easier to clean and maintain too. The slight compromise in gear range is more than made up for with simplicity and durability.
I've also been experimenting with 1x7, 1x8, 2x8 and 2x7 set-ups on various bikes. I'll probably switch to a low geared 2x9 if we get any snow this year.
Having worked on several 10 speed mountain bikes over the past few months, the common problem I have found with them is that they are much more affected by otherwise minor problems.
For example, even slightly sticky cables or a slightly bent mech hanger plays havoc with indexing. The sprockets are closer together so indexing has to be that much more precise.
I also think that 3x10 setups are pretty pointless. Sure you have a very wide overall ratio range but there are multiple gear replications and the closer step ratios mean that you're constantly changing gear anyway. The narrow chains also seem to wear out significantly faster than 9 speed alternatives.
Shadow mechs are also awful whether 9 or 10 speed.