Parks and such are pre-programmed in many units -- depends on what kind of you purchase, as well as what kind of maps it supports. The ones we use in our cars and in Justin's rental aircraft have everything from parks and gas stations to restaurants, hotels and shopping centers. Mine has rest stops, which is nice when you get out in the boonies and someone's asking "Have you seen a rest stop sign" every 15 minutes.
For those like me who get turned around easily, a GPS is a godsend even in a city I've lived in for over 2 decades (though I'm 31 so I wasn't driving that whole time!) Also, I often leave mine on and it provides more situational awareness than normal driving -- "Ah, that's where thus-and-such is..." or "Cool, there's a Tai restaurant within 1 mile of here!" It's an exploration tool as much as a navigation tool.
For hiking, I have a topographic unit that I use in conjunction with a park map and (though rarely used, since my GPS has a built-in electronic compass that is easily calibrated) compass. I've discovered 'new' (undocumented) trails that link up some of my favorite rural parks with this device, whereas I wouldn't have bothered following the trails without the GPS due to not knowing how far I might end up away from where I parked my car (these are solo hikes, so as a female I like to know where I might put myself, especially if I'm several miles from familiar territory and my vehicle).
For exercise, I have a wrist-worn unit that calculates calories burned and keeps a running log of all my exercise activities -- I need to post a logbook entry from that soon. It proved VERY useful during the rehab after my knee surgery, being able to see improvements in my pace (miles per hour) and distance travelled.
GPS units are tools just like computers. Some people still do their taxes with a pencil, paper and calculator. Some still write their letters with stationary and a nice fountain pen. Etc. No way is better or worse, but each fills a need.
Justin and I are obviously geeks, so we keep buying units that fill a need we have. The average person can do well just with one handheld unit, since even handhelds can be used in vehicles for travel as a preventive measure of having to stop and figure out where you are exactly.
We bought our cheapest GPS units, the Garmin Rinos which have GMRS radios built in (great for families -- parents keep one and give the other to the kids, and can keep track of where they are and talk to them when its time to come back to camp). Cost? $49 per unit, on clearance. Deals are everywhere. Considering what people pay for cellular phones, cable tv and other luxuries, a GPS falls right in line with all that.
