I like the lack of sympathy, "If at first you don't succeed, you fail."
If you look for gameplay videos on Youtube, the voice has even crueler things to say. "If you find you are tired from thirst, feel free to pass out."
Portals would make two things possible.
First, you could create a perpetual motion device with two portals facing each other, one slightly higher than the other, building a downward-sloped Hot Wheels track in an infinite loop, installing a water wheel over it, and pouring in some water.
Second, you could sixty-nine yourself. The impossible is easy.
Obviously "Portals" aren't likely to be showing up in our universe any time soon. But one could posit a universe where they existed, but didn't enable perpetual motion... like if they took as much energy to operate as the mass of the object passing through times the delta in potential energy. Which is less contrived than it might sound, to me it sounds reminiscent of the relationship between magnetism and electricity. I have a theory that if there's ever any kind of "gravity shield" it might operate under similar restrictions. TANSTAAFL!
One important thing to note is that in Narbacular Drop-- and this feature isn't necessarily reproduced in Portal-- you can cast a portal through another portal. That is, gazing through one portal, if you see a suitable surface, you can re-cast the other portal to that surface. With some foresite, it makes some of the levels incredibly easy. Also, yeah, boulders don't spawn consistently at all, so if you feel like something's missing and a boulder could do the job, restart the level.
Also, if you happen to have Half-Life 2 and have paid the $10-15 for "Garry's Mod," the (single- or multi-player) sandbox environment for Half-Life 2's wonderful physics/game engine, "Source," the portal-gun has been reproduced by fans, and there are some amusing videos on youtube to prove it. The Garry's Mod portals are a little error-tastic, as they don't limit what surfaces you can cast them on, and they're also pretty liberal when it comes to letting you through if you hit the portal slightly off-center. The momentum-preservation effect of the portals also means you can push the physics engine over the edge and crash the game, though it's fairly robust-- crashing it might take a bit of work.
I played around with Narbacular Drop a little last night, fun!, although keyboard control isn't as smooth as I'd like. I wonder if some of the jerkiness is because it's rendering through the portal. I wonder if opaque portals would make the game much harder.