“Do other people have the same problem with their GPS units?”
I actually utilize the GPS service through my cell phone...it’s called VZ Navigator and I haven’t had any dropped GPS signal yet.
“Do other people have better experience with Tom Tom or another manufacturer?”
I haven’t owned a standalone GPS device so I wouldn’t know.
“Is this a problem that I will have to deal with no matter what brand of navigation system I use?”
I doubt it.
I bought my wife an inexpensive Mio 310c last year. It has been very reliable and easy for her to use. I am in the process of updating the maps. There is a users web site that shows how to hack the system to exploit capabilities not marketed - I may pursue some of those once the warranty expires.