The worst casual game that I've had so far was against a player who couldn't really shuffle cards in sleeves, and all the agendas were clumped at the bottom of the deck. It wasn't deliberate cheating, just sub-par randomization, and I really should have asked to shuffle her deck for her a few times before the game started.
I have trouble getting that: shuffling sleeved cards is actually easier.
I also don't see a problem with the floor rules not explaining how to properly randomize a deck, because it is not in the scope of the rules. I have nothing against them containing suggestions on that point, however.
Making piles doesn't do anything for randomization, but it breaks clumps (and if you're mathematically minded, it can help you check your deck size). Some riffling after that and you should be good to go.
Coming from an MTG judge with experience debating this question I'll point out something.
There are two scenarios to pile shuffling, either A) The player randomizes the deck totally, thus rendering the pile shuffle a useless step. or B) The player fails to randomize the deck totally, and the 'clumps' of card order are apparent. This is cheating. There is no real middle ground here. Choosing to arrange the deck in an order that benefits someone, then undo that work…well, thats a poor choice.
'Clumps' can, and will, occur through valid shuffling techniques, as will a perfect 'pile shuffle' apperance some times. When an opponent watches you pile shuffle, calls for a judge (or TO) and says 'my opponent did x cards in a pile, can you please check his/her deck to see that (s)he's not cheated and failed to randomize it'…he's fully in his/her right because he/she SAW you arrange it. Now even random chance can catch up. Now, the two options will come up, there will be no order apparent and everything will be 'ok'. Or…a pattern might appear, and that's bad news.
So why risk it? Why EVER put your deck into a known pattern in front of your opponent, regardless of how well you think you're going to shuffle. Just shuffle like mad, 8, 10, 15 times if you think clumping is going to be an issue. Post game when they may be organized a little by your play, make sure to shuffle those first, then shuffle them all back into the deck itself. No pattern, no problem.
Just my 2 (experianced, having to boot foolish pile shuffling players getting caught) cents.