I've had it on my BB Curve 8330 for just over a month now. I bought the 1 year subscription a little too hastily and should have kicked the tires first. It may be useful as a backup, but I wouldn't rely on it for much more.
Cache descriptions can generally be browsed quicker for me using GC.com's WAP interface => wap.geocaching.com
I hate the way that there doesn't seem to be any way to switch applications when running Geocache Navigator. I'm constantly switching apps, and having to start over every time with Navigator is a pain. Maybe I just haven't figured it out, but it's not working for me.
One of the things I was hoping to see was links to images that people embed in caches. Sometimes this is the only way to solve/find a cache in the field and if the images aren't handy, you're out of luck. No go. I still have to navigate to the regular GC.com page (can't do this in the WAP interface either).
On the topic of field notes, I manage logging via GSAK, so this wasn't a requirement for me. However, I did want to take advantage of GC.com's integration of Field Notes and Twitter (see www.geocaching.com/my/sharing.aspx
). This turned out to be a no-go as well. Only field notes posted via groundspeak's iPhone geocaching app will work. We Canadians can't use the SMS TextMark service, so we're out of luck there too. I've come up with another workground which doesn't involved Geocache Navigator to meet my requirements, so this another reason for me not to use it.
So, in summary, if I'm out somewhere and don't have my GPSr with me, I might consider using it if I know there's a cache around the block somewhere, but beyond that I don't see me ever using it. And at $40/year, I doubt I'll renew my subscription when it's up.