Mark Liberman of Language Log breaks down the use of "Per Usual" in Eric Umansky's "Today's Papers," which appear on Slate.
Umansky appears to have written 550 of the 2481 Today's Papers pieces in Slate's archives (can the feature really have been running for 2481/365 = 6 years and nine months? I guess so!). Each of these pieces is around a thousand words long, so Umansky has used per usual 4 times in 550,000 words, or about 7.27 per million words, whereas the other Today's Papers writers have used the same phrase 0 times in about 1.93 million words (and yes, I know that it is silly to use three significant figures when my estimate of article length has only one...). If the other writers had the same propensity to use per usual that Umansky does, we would have expected to see about 14 instances. Without doing the statistical calculations in detail, we can guess that 0 is significantly different from 14, over this span of time and text.I'm not sure what it signifies, but it's interesting to note.