It's all pretty much horses for courses really, certainly with the new 10 speed cassettes going up to 36t it makes going 1 x 10 that much easier, personally I prefer a 2 x 9 set up for off road as the big ring is pretty much surplus to requirements & the extra ground clearance plus lack of teeth to shred your legs is a worthwhile benefit. Going single ring up front just doesn't have enough worthwhile benefits in my book & the lack of the low gears for hills, mud & other tricky terrain doesn't make much sense, seems more of a trend than of any practical advantage.
There was a post on stw showing that going 1x9 only loses the lowest two ratios in the granny ring and the top two ratios in the big ring.
May not be many ratios lost but 32t cassette x 22t chainwheel = 18" gear, 36t cassette x 32t chainwheel = 23" gear, may not sound much but that is 29% difference in ratios (& a massive 45% difference if you stick with a 32t cassette!), so I'll keep my granny ring thanks.