I'm heading to london next monday and I've loaded all of the maps. I don't plan on having a data connection, so how useful will this be?

Will I be able to use the GPS to locate where I am at?
Will I be able to enter a location, and get walking directions to that point using GPS?

Yes, as mentioned in other threads, use GPSJinni to acquire your location. It won't time out like OVI maps and it's desktop widget do. Once it locks, you can use whatever you want to navigate around. You could also probably leave GPSJinni on in the background to maintain a lock, although if you don't, it should reacquire its position faster on subsequent usage.

awesome, downloading it now.

tried and used it a few times in london and it is good...only thing missing is the navigation but i can live with that as long as i am on foot...