Garmin makes a very fine unit. I think the biggest problem is that there are many GPS' out there and almost any price brackets.
I have a etrex legend, it is great for making maps. My rescue unit went to Rhinos, very nice. Also there are GPS that talk with other GPS, great for group outings. Let you know where other members of your team are.
I use my for traveling too. I don't need a talking GPS. The Ability to upload and download maps are important to me. My first GPS a Loran, did not do that..... ugggg
I have a Tomtom 300 not had many problems with it lets put it this way when coming home from a certain barracks i got home no fuss but my father has a navman and it kept telling him to go back on himself even though he knew he was going the right way. Cost about £200 only annoying thing about them is the map updates are about £90 i think.
My father has a 510 in his car and he had no problems with it yet. But as seventy6er said, it's a bit overpriced compared to other systems and for what you get when you buy it. I just bought a Navigon 7110, a bit expensive but it's totally worth the money.
I've been using Garmin GPS receivers of various models for around 15 years, in my opinion they are still the best, and their SATNAV systems are in my opinion better than TomTom. TomTom is weakened by it's bulkiness and inferior mapping software*, not by it's functionality.
* I refer to the European models - I can't speak for North American software which is probably a totally different mapping package.