node blog (solution 1)

a example wold be this new blog theme module (copied and modified from the original module):

function blog_theme_help($section) {
switch ($section) {
case 'admin/modules#description':
// This description is shown in the listing at admin/modules.
return t('this module changes the theme used to display a users blog to the users default');
}
}

function blog_theme_init() {
global $custom_theme;
$nid = arg(1);
$node = node_load(array('nid' => $nid));

if (arg(0)=='blog' && arg(1) != '') {
$uid = arg(1);
$themes = list_themes();
$account = user_load(array((is_numeric($uid) ? 'uid' : 'name') => $uid, 'status' => 1));
$custom_theme = $account->theme && $themes[$account->theme]->status ? $account->theme : variable_get('theme_default', 'bluemarine');
}
else if (arg(0)=='node' && is_numeric(arg(1)) && $node->type=="blog") {
$themes = list_themes();
$uid = $node->uid;
$account = user_load(array('uid' => $uid,'status' => 1));
$custom_theme = $account->theme && $themes[$account->theme]->status ? $account->theme : variable_get('theme_default', 'bluemarine');
}
}