"If you just use them to connect to the Arduino (aka, no high loads) your fine."
Not always the case. May switches (not those in the link) are made with Silver Oxide contacts and will corrode over time. They need at least 10mA to keep them happy. Switches specifically designed to switch "logic" levels will have GOLD contacts and you can't use them for high current.
If you want a robust solution, use a logic level Optocoupler such as the H11L2 and have the switch turn on the diode. Then, you can use the Internal Pullup on the Arduino. Of course there's a net inversion, so you have to complement at some point.
@rmetzner49, you're right but then we're talking minimal specs instead of max. But unless you're using really massive switches I never had a problem with it. PCB tactical buttons don't use fancy materials (most of them) as well. And these are not mega big so I don't see a problem. I know, not best practice if you design a real/commercial system but fine for hobby projects.
But why on earth would you pass it trough a opto for no reason? Yes, I call pulling more current no reason If you want more current, just use a bigger pull resistor.
Some of the systems I've designed were Automotive, so your comment regarding the Isolation works in YOUR case. If I'm looking at a 12V input for example, I would certainly feel better using the Opto as a level shifter. Besides, it gives you some noise immunity since a mere voltage spike from some coupled line wont turn on that Opto. With the Opto there, it's very unlikely 12V will meet an input pin. Letting the smoke out of your Cortex isn't that much fun to watch. The H11L2 I cited even has a bidirectional LED, so you can connect it through a resistor to 24VAC for example with only an adequate dropping resistor.