Well, I bought myself the new Garmin 410 last fall. I have used it several times, and have a rather succinct review: its the same as the 405, only improved. (For my love/hate relationship with my old 405, read here.) The undeniably biggest difference is that the touch bezel no longer goes psycho crazy when it gets wet or sweated upon. I haven't run in summertime humidity with intense sweating yet, but I did run in the rain with it. And so far it acts normally. That is it rightfully reacts to a touch from a finger and not to wetness. Also the fact that it is wet does not cause it to freeze or lock up.
So that is an improvement. Other than that? Seems to me to be the same watch. Looks the same, same strap (although it does come with a soft strap). Same interface and screens and software (although it is supposed to pick up satellites better, but I haven't noticed). I am a little frustrated in that I had all of my settings and screens set up on my old watch, and now I have to figure them all out again to get it to the way I like it.
Sort of an anti-climactic review I know, but it really doesn't feel any different from the 405, other than the fact that the 410 works when it is wet. That is a big improvement, but worth dropping 360 bucks on? If you have a 405, I wouldn't run out and buy the 410 unless you need a new Garmin; my old 405 was kind of getting long in the tooth; I bought it the first couple of weeks 405 was on the market in April 2008, so I bought the new 410 instead. And honestly, the 410 feels like the watch the 405 should have been. Fewer hardware meltdowns, brain freezes and general instability. But still is that worth the upgrade? Eh, probably not.