The 2009 NAV unit is superior to the early years. And he XM weather radar feature is excellent.
I wish I had it on my 2007 so much that I am probably going to add a garmin 378 or 478 marine unit that will be both my XM radio and weather tool. It will be a little superfluous to have two GPS's, but I guess a lot of people do the same thing because they dislike the stock NAV unit.
And no, you can't just toss the 2009 software onto the earlier units. At least so far, nobody has found a way to hack the sytem to do so. The 2009 uses the the NT mapsets, so that's a big problem right there.
One other annoying new concern: Garmin is apparrently no longer going to update the non NT mapsets, so City Navigator 2009 will be the final mapset available. You can replaceyour earlier mapsets withthe 2009 version if you buy it, load it on your PC, and then upload to the card (you have to make sure you pull the unit number off the device in your trunk (just loosen the cover with a screwdriver and you can see the number). the 2007 and 2008 Wings came with 2006 maps, so it's worth doing.
$89.95 for North America non NT 2009 maps from these guys. (don't just buy the upgrade, you need to install the whole package on your PC to then transfer to your NAV card)
It's item # 010-10474-00 Ignore the warning about not using to update preloaded garmin units....that does not apply to the Wing NAV unit card.