I use the Garmin StreetPilot 2610 (the CompactFlash version, not the 2620 mini-hard drive version) in my truck to get me to new addresses every day. I run a DirecTV installation company. It works perfectly for me, and saves me a lot of time, especially if I have to go to an unexpected destination in the middle of the day. I second the recommendation to go with a flash-memory model over a "pre-loaded" model that uses a mini hard drive. My GPS unit takes a beating in my truck and keeps right on going, but if it had a hard drive, I'm sure it would be dead already.
All GPS map data comes from the same source (NAVTEQ), so you'll find that many newer streets aren't in the system yet, and you also won't find them on Google, Yahoo, Microsoft, or Mapquest either, because again, the info all comes from the same source. Hopefully, since most of the US has now been mapped, updates will start coming in faster, but so far, things are typically 2-3 years behind.
-Troy