What is it with PDF’s, anyway?!?

I slacked off a bunch over the last couple years, because I had so much good work coming in.  I didn’t really have to show my portfolio, because I was already getting enough people calling me!  Well, I’m sure you’ve noticed that things aren’t the same as they used to be, thanks to the economy.  

I don’t have the luxury of sitting around and waiting for the phone to ring.  I have to send out promos and portfolios.  I have to knock on doors and actually market myself again.  It’s not that bad, I guess.  It’s just part of the business.  
I will say this about today’s marketing:  Things have changed over the last couple of years.  Everyone I ask about seeing my book says, “Do you have it on PDF?”  Everyone I call about sending over a portfolio says, “Can you send me a PDF?”  Everyone that says they would love to see something from me, follows up by saying, “Send me a PDF.”  
When/why did things change so fast?  Is it the ability to view work from laptops, PDA’s, and cellphones?  Is it the ability to ignore the bad/boring books without a face to face meeting or a follow-up call to pick up a physical book?  Is it the ability to glance through several submissions faster than flipping through real pages could ever do?  
Whatever the case, I’ve sent out several PDF’s lately.  I guess it saves me money of printing costs, but it just seems less personal.  Touching a page, thumbing through images, stopping and looking at a beautiful image as light hits the paper…  
I say all this as I listen to a vinyl record and wrap up my business day to take my boys outside to actually play and run around.  I’ll send those virtual pictures, but I will mourn the death of the printed portfolio.  
By he way, I started sending this basic promo as a PDF, but I guess I’ll need to build a full portfolio to email out.  Hopefully, this gives potential clients enough of a taste…  maybe enough that they’ll actually request an old school printed portfolio?