If I was just getting ready to create a PP for myself today, I would probably dip a toe into the water by dollar cost-averaging every few months. Depending on the investing time horizon I was looking at, I'd also change the weightings to be stock-heavy and bond-light... at least for the time being. So only a percentage of my portfolio would be a true PP, with a "modified PP" sitting on top of it. My PP is all ETFs, incidentally. In fact 2/3 of my retirement money is in ETFs, with the only mutual funds we own being in our 401K accounts.
This is pretty much what I did a year ago when I put a portion of my retirement assets into a PP. I don't believe in embracing any single investment strategy for 100% of my portfolio, so I carved out a chunk that would be a dedicated PP and then turned the rest into a VP that is like a modified PP in some ways, with extra stuff thrown into the mix.
After reading dozens of investing books and academic white papers, I've settled on a few other approaches that I like in addition to the PP. I like the Boglehead approach, the Ivy Portfolio approach, the All Weather approach, and the Merriman approach. I tried to come up with a way to take the best features of each of those approaches and make a portfolio customized to my liking. What I wound up with looks more or less like this:
5% Cash
5% Commodities
10% Gold
10% LTTs
10% Total bond market
10% REITs
30% US Stocks
20% Foreign Stocks
As you can see, only 35% of my portfolio is a PP (5% Cash, 10% LTTs, 10% Gold, 10% Stocks), with the other 65% leaning heavily towards stocks at an additional 40%, 10% in REITS and 5% in Commodities on top of that, and 10% total bond market to round it off. I basically didn't like being without REITs and broad basket commodities in the PP, and I wanted some broader bond exposure. Plus I have a 15-20 year time horizon before I'll begin withdrawals so loading up on stocks makes sense for me based on historical performance.
I should add that my stock investments are all indexes, but I have a mix of different things besides simply a total stock market fund or S&P 500 fund. I also have a High Dividend fund, a Low Volatility fund, several Value funds, and an Equal Weight fund. On the foreign side I have developed markets, emerging markets, large caps, small/mid caps, and low volatility funds. Basically I have a "core" total market fund, then I tilted the rest of my stocks towards funds that I think have the best long-term chance of outperforming the S&P.
I may be unusual in having nerves of steel, since I didn't sell anything when 2008-2009 hit. Sure it made me sick to my stomach, but I knew it wouldn't last so I started shifting more heavily into stocks the lower they went. I viewed it as getting a bargain, and I've since become very contrarian in my investing outlook. As soon as something in my portfolio goes down, my immediate reaction is not to panic and sell, but rather to purchase more of it to bring down my cost basis.
Sorry for the long post, but I've been off the message boards for a while.

The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary.
- H. L. Mencken