[development] Documentation needed: new format for update_N hooks

[Angela Byron]

Post-schema API, I assume we no longer do crappy stuff like this in  
our update_N hooks:

switch ($_GLOBALS['db_type']) {
   case 'mysql':
     // blah...
   case 'pgsql':
   // blah..
}

and probably are now supposed to use db_$FOO functions...but we  
really need some kind of instructions at the module update page  
(http://drupal.org/node/114774).

I'll volunteer to write this, but I need to know:
a) Is system_update_6022 a good example on how to perform database  
updates post-schema patch?
b) If so, would a reasonable way to document this be to take the  
update code from http://drupal.org/node/115267#comment-249052 and  
compare it with this?

Thanks...

-Angie