Yup, had the first ride last week as 1×9, although as I am truly fat and unfit I went for a 28t ring on an 11-34 on a 29er. Figured that as I rarely use anything but middle on my trails, with occasional granny, I wouldn't be losing much.
In reality, it was great. No hassles and it meant winching up some of the steep stuff pushing a bigger gear. Duh! Failed a couple of times but figure I'll get stronger.
I do seem to have developed a dreadful crackng/clonking noise & feeling through the drivstrain however. Not sure what the hell that is, hoping a new cassette and chain will fix it!