I know this is an old thread but I thought I'd post a follow-up for the Google archives...
The building owner contacted the power company and they (unknown to me) attached a monitor for 18 days (!) and then sent us a dozen graphs that their engineer had reviewed. (Peak/Min/Avg for Voltage, frequency, and current for all three phases plus neutral.... I was glad to see detail.) There were a couple minor events, all brief sags, and the engineer had noted causes for each (one was severe storms, another was a phase outage "elsewhere on feeder") Ultimately they determined everything was within normal but I did feel like they took it seriously at least. It was actually interesting to look at a couple weeks of activity.... there are predictable voltage curves at various times every day and week to week. Phase 1 and 3 stayed between 119 and 125 for the entire period; On day 6, Phase 2 became much more exaggerated (between daytime/nighttime) and barely squeaked in between 115 and 126 for exactly 7 days - and then was perfectly normal again. Maybe it was just a hot week.
BTW since then I programmed my computer's UPS Battery to write voltage to a spreadsheet - all I have is voltage but my residential power is FAR more stable, usually varying only a couple degrees in a 24-hour period.
We've had no other equipment failures but a number of light bulbs burned out one night in the restaurant just a couple weeks ago. I'm surprised there's not a whole-building surge unit like I've seen other places, and they don't seem extremely expensive, so I might recommend they pursue that.
.... so there you go.