I will keep my Mio GPS, and probably buy a newer one in the near future (my Mio is already 3 years old, and even the maps I updated are now 2 years old). My Mio also has over a million POIs (points of interest). It easily found various sports stadiums, night clubs, businesses, etc.. in various cities around the country. Not all GPS manufacturers are so helpful, and obviously it won't find new/moved businesses, but having a GPS that doesn't depend on a data connection is the only reasonable and safe way to travel.
This new Google map will be great for driving around a large city with good connectivety, but as for long trips or those out in the middle of no-where, the requirement to have a constant connection for visual maps will be an issue. Your phone can't cache everything it needs. It might cache the route, but that's basically like a Google maps you printed off at home. Plus, what if you are in a new town, and need directions to a specific store, won't do any good if you don't have a data connection, you can't cache a route you didn't already look up.
If you have a regular cell phone and GPS, but still want Googles listings, try this: use Google SMS search (send a clear text message to GOOGL, like "McDonald's in Plainsville, KY"). I can find up to date listings for businesses. Then, using my unconnected GPS, I just enter the address Google gives me, and viola, directions. No Android or Data connection needed.
That said, I'm sure once T-Mobile releases Android 2.0 for my G1, I'll at least give the new google maps a try.