use krumo() in session viewer and pretty up name/id presentation. if you haven't installed krumo() into your devel module, you are missing out. See the README. D6 only, until someone cares to backport.

use custom menu instead of a custom block. you will need to enable the 'development' block on admin/build/block page. still need to dynalically append querystrings to a couple menu items.

of the switch user block.

block via a variable ('devel_switch_user_list_size'). No UI for this (yet).