Trademarked:
My tip, which might seem a little contradictary.... is to leave your smartphone at home or the hotel when you travel. I was pretty much flabbergasted when I went on vacation by the amount of people who, rather then notice all the amazing sights and sounds around them, had their faces staring at their phones the entire time. Smartphones are incredibly useful tools, but its important to remember all the other amazing things surronding us on our vacations.
"Stop and smell the roses" is always good advice. I'll respectfully disagree with your advice, though. It's hard to blame a tool for its users' shortcomings, so it's really the behavior that needs addressing, not the availablilty of the equipment. You could equally argue to leave your wallet in the hotel to prevent overspending on vacations! 
As long as you have the willpower not to continually check your email or Twit your experiences every 5-1/2 seconds (then again, it's your vacation- if you want to spend it twtting, who am I to tell you not to!) the smartphone can be an invaluable travel guide/assistant.
I ALWAYS take my smartphone on vacation because it can actually help enhance the experience. Besides having important travel information at your fingertips, (like reservation confirmation numbers, telephone numbers and addresses of your hotel, as well as museums and other sights you don't want to miss,) you can get travel related info on the move. I've checked Yelp to access restaurant reviews when deciding between two unfamiliar places across the street from each other at lunchtime, checked Tripadvisor for reviews of hotels when making unscheduled stops- I've even Pricelined a cheap hotel room on the run, when a longer than anticipated stop on a driving vacation unwound our carefully planned itinerary and forced us to stop for the night in a city we hadn't planned on stopping in.
And that's all in addition to the obvious things like navigating your way around an unfamiliar city with Live Search Bing or Google Maps, or using it to ensure your cabbie is taking at least a semi-direct route, as opposed to jacking up the fare on a slow day by driving obvious out-of-towners like ourselves in circles. (Covertly checking the GPS route and asking a seemingly knowledgable question like "Interesting! Whenever I rent a car when I'm here, I always take Jackson Drive- is this way faster?" will snap a cabbie back into honesty mode virtually immediately with a mumbled excuse about "construction" or "traffic.")
My latest money-saving travel trick (or even when home) is to download online coupons into my phone browser that I didn't remember/think to print out ahead of time, and then present the phone in lieu of the printed coupon. If they demand a paper copy, I try to "shame" the establishment into accepting them by (rightly) telling them that isn't "green" to waste a piece of paper on an internet coupon that only be used once. If shaming doesn't work, I offer to let them photocopy my phone's display on thier photocopier (that doesn't actually work, BTW, but it generally either calls their bluff, or they try, fail, give up, and just give me the discount to shut me up.)
Every now and then I get a tech enthusiast who really grooves on the coupon-on-phone idea, happily gives me the discount, and tells me he or she plans to start doing it as well from then on. (Sometimes I even get the wiseguy who tells me he needs to keep the phone as the "hardcopy" of the coupon if I want the discount, then laughs and gives it to me.)
(I actually used to keep a small battery-operated thermal printer in my car that printed from Windows Mobile devices via infrared for printing coupons on the run, but that's been made obsolete by the lack of IR ports on modern devices. Not a big loss- the printer only set me back $15 on a closeout from Geeks.com three or four years ago. They still had some left three years later, last time I looked! It's called a Sipix A6. Now it's the portable printer for my netbook. A small $5 eBay USB-to-IR dongle for the netbook made it possible.)