We've actually had two of our vendors, Tippingpoint, and Procurve, bought by HP. HP has pretty much just tacked "HP" in front of the name and left them alone and it has been pretty close to dealing with the smaller companies. In fact the most user-visible change has been the SSO integration for their web services. Of course I don't interface much with sales on those products.
My biggest concern, were the deal to go through, would be the fate of the MAS platform. The Procurves were great bang for the buck but lack a lot of the configuration flexibility afforded by the MAS since they stuck to the cisco mold, and we've been warming up to the MAS's daring break with that tradition since we bought them.