I do a lot of research as part of my training development and delivery. I want to stay abreast of what's going on in my industry, my students' and customers' industries, the ECM/RM/IM industry as a whole, etc.
Many times that means looking to the solution provider community. And many of those require registration, which I think is silly. However, sometimes the resource looks interesting enough that I will go through the rego process anyway.
Which brings me to my rant. An increasing number of these registration pages will not let me register with my main email account because it's a Gmail account. The reason of course is that many of us want the goodies without paying for them - that is, I want to read that white paper without having the vendor a) know who I work for via the email domain and b) contact me. However, I've been on the same Gmail account for over a decade. It is in a very real sense my permanent, primary, best email account because who knows if I'll be at the same employer this time next month? But I know that my Gmail account will work.
So vendors. I understand that you think that content marketing, a paywall, a Hubspot landing page, etc. are ways to qualify me. You're flat-out wrong, but I understand that you think that. But having me register, and then telling me that my email address is unacceptable, is a great way to ensure that neither of us bothers the other again.