How it works:
When you start moving forward addon checks if you have minipet summoned already, if not and if you're not in combat and not mounted (etc.) then it will summon one from your list of favorite pets.
In 5.0 it's the same, Ctrl-Click can set pet as favorite along with blizzard's dropdown menu.
ToC Update to 60000
Fixed for API changes in 5.1
Blizzard is now using petGUIDs instead of petIDs, hence character-specific favorites has been reset to use new format.
5.1: Character favorites
5.0: MoP update. Thanks to petbattles api changes, addon is a lot more reliable now.
4.0: Cataclysm update. Also fixed bug when you can't summon if only one pet selected
1.4: Cleaned up, db format changed, various fixes
1.3.2b (by Robsato):
Rebuilding summoning list after new pet is learned
Does not try to summon a minipet anymore when flying or when in a vehicle.
1.3.2: Timer edit box now will hide when switching from pets tab
1.3.1: Bug when game freezes if only one pet selected fixed; Keybinding for summon fixed
1.3: Timer for chaning pets, pet database reworked, bug with ids when new pet is learned should be fixed (not tested), now only CtrlClick to select/deselect pet
1.2: Borders and checkbox in pet frame, no need for console now
1.1: +pet -pet removed, now addon only deals with pet IDs
1.0.3: multilink +pet -pet
1.0.2: added option to enable/disable addon