1) not sure about safari, but the issue with IE is in the way it handles caching of images when called from javascript. the short description is that for each marker that is created, it will try download the marker images, caching in IE is fairly slow, so the images will not get cached while the script runs
you can try adding the marker images directly to the page using image tags to force IE to cache the images which should speed things up:
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_pacifica.png" style="display:none" />
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_shadow.png" style="display:none" />
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_pacifica.gif" style="display:none" />
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_pacifica_mozprint.png" style="display:none" />
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_shadow.gif" style="display:none" />
<img src="http://www.yourdomain.com/google_javascript/images/traditionalflat_pacifica_transparent.png" style="display:none" />
2) when it zooms out to show all of North America, it means that the last address it tried to process through the geocoder failed lookup so it is drawing the default view. double check the validity of the addresses.
3) if you enable driving directions, but do not enter a starting address it will not open the balloon on load
4) the balloon uses a span tag, for example:
infowindowtext: '<span style="font: 12px Verdana, Arial, Helvetica, sans-serif; color: black;"><strong>Address:</strong><br />2001 Cornwall Street<br />Regina, 1 S4P 3X9 Canada</span>',
you could add a width attribute to increase the width:
infowindowtext: '<span style="font: 12px Verdana, Arial, Helvetica, sans-serif; color: black; width: 400px;"><strong>Address:</strong><br />2001 Cornwall Street<br />Regina, 1 S4P 3X9 Canada</span>',
5) I'm not quite sure i understand what you are getting at with this last question.