To get it into google earth I upload the info to http://www.motionbased.com
and follow the links from there.
You can then export it in a format that works with Memory-Map, if you have that software.
Tall buildings do affect the watch, had that problem at the start and finish of the Dublin Marathon the other year. My 305 also seems to have a problem working out where I am when I press 'start', but it's usually pretty accurate after that. Just need to compensate for an extra 100m or so.
For marathons I always set two of the displays to show average pace/lap and average pace/total. Good bit of kit.