I've had Point-of-Sale installed for just over 3 years now. One spiffy thing is that it is pretty easy to pull out sales data in specific and in general. So, I yanked all of my book format sales for DC this morning (no comics included!), and found out that over the last 3 years I've sold ~$183k in dollars of DC TPs.
Of that, $88k is from Vertigo branded books. $68k is from books with the DC bullet on the spine. $25k is WS, and the various imprints there. $2k is from "other" imprints (Piranha, Humanoids, and so on)
If you were to divide the WS books into "closer to DC" and "closer to Vertigo" (ie: PLANETARY, PROMETHEA, ASTRO CITY, EX MACHINA, and so on going in the "Vertigo" pile, AUTHORITY and all of the cape books going in the "DC" pile) about $21k of WS' business would be on the Vertigo side, with $4k on the DC side.
This would put "Vertigo-esque" material at roughly 60% of my DC book sales. That percentage probably flips entirely the other way when looking at periodicals (actually, probably worse -- maybe as high as 80/20, though i don't feel like yanking that data out)
About 11% of my "DC" book dollars, however, are from WATCHMEN alone. It has the DC bullet on the side. If it had been published after Vertigo existed, I suspect it would have Vert branding.
Another note: I have to purge somewhere between 10-15% of my DCU books each year when they go 12 months without selling (and we're racking, at this point, maybe 60% of each month's brand new DCU TPs?) -- I've purged like five Vertigo titles ever for lack of sales (and I rack 100% of what they release)
Anyway, Vertigo books are far more important to my book-format bottom line than DCU books.
(PS, I'm stuck at the store for 8 hours tomorrow, so I'm going to try hard to do a comprehensive week-in-review column for this week's comics then)