I go through Ad Review at least every couple of days using the Netmeg recommended procedure of progressing through them using the 1, 3 and then 7 day filters.
I find ~50-150 new ads every time I do a review and block all but a handful each time because they are in Chinese, Russian, spammy, are poorly worded/designed, have phone numbers and/or, of course, are totally off target.
This is also on top of having all sensitive categories turned off and blocking all of the 50 categories allowed in General Categories as an attempt to limit what actually does land in Ad Review.
At least every week or two I also try to go through every ad to find those offenders that have snuck through cracks. Often, this can mean going through as many as 500-1000 ads. I feel it's worth the time.
When I don't do this, the effect on CTR is immediately apparent. As every page view is a click opportunity, even well targeted ads may not directly appeal to that particular visitor but totally off based ads are very unlikely to have any appeal at all.