I can sometimes shoot "acceptable" images at 1/30th with extreme care (leaning on a post or something) but do expect them to be perfectly sharp. But for critical sharpness or when I expect to be doing some enlarging I try not to ever got below 1/125th regardless the focal length and follow the old 1/focal length for lens longer than 100mm.

About 10 years ago at a multi-day photo workshop there were a number of participants boasting about hand holding down to 1/30 or even 1/15. Their chromes on the light table later in the week proved otherwise.