0.67 Additions Specifics:
25 new heroes
Quote from: 6 new settlements

    Griffinhill by mukk
    Falconpass by Berpol
    Esgaroth by jacob25
    Grenlandsby by Folthrik
    Diavolonia by Diavolo
    Drunadd by Datver

8 new empty settlements

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Mercenaries are like the Adventurer Faction.  They do not claim settlements.

There are mercenary bands that will roam around the map.  You can talk to these and if you have enough money you can pay to have them join you.  Mercenary bands will join together to make bigger mercenary bands.  Each time you pay for mercenaries that faction will like you a bit more.  High relation with the mercenary faction, and High persuasion skill, lowers the cost of hiring them.

Heroes can use their extra gold to buy nearby mercenaries as well.  Heroes can start with gold if they didn't use all their allotted gold from their equipment buy.  Heroes can gain extra gold by selling their prisoners to settlements.

Besides mercenaries, some work was done on adventurers, peasants, and bandit factions as well.  There are now small adventurer parties, and heroes who are part of the adventurer faction collect nearby adventurer parties into their party.  The player can get these small adventurer parties to join them for free if they have high relations with the adventurer faction.

The same is true of Bandit Heroes with bandit parties.

Peasant Heroes tell nearby peasant parties to go to their settlement.

Mercenary Heroes get mercenary parties to join them for free.

When a settlement is raided the peasants there slowly trickle out as mercenaries, peasants, and adventurers.

When prisoners revolt, if they are successful then the prisoners abandon the settlement in groups of mercenaries, with bandits remaining behind as the bandit party.

Large settlements like Custow have their peasants leave to become Mercenaries, Adventurers, and Peasant parties.

The Bandit, Peasant, Mercenary, and Adventurer troop trees have been filled out.  The top tier troops are no longer upgradeable to.  In order to create such you must meet certain requirements, and they cost money, and then you must spend time to make them.  Also, you can now train men or women specifically rather than always both at once.
Currently only the Royal Bodyguard and Flurries are implemented.  To make Flurries you must have atleast 1 Speedshooter in the garrison, 1000 gold, and a manor, then you go to "Organize Population", then "Train Military" then "Train Female" then "Train Flurry".  To make Royal Bodyguards you must have atleast 1 Bodyguard in the garrison, 5000 gold, and a Castle Town, then you go to "Organize Population", then "Train Military" then "Train Male" then "Train Royal Bodyguard".

That's most of what the "Mercenary Faction added" part means.

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Whenever a King/Queen is unoccupied and moderately strong, they will look for nearby enemy settlements to conquer.  Whenever they have a settlement targetted to attack, they call all their Lords/Ladies/Patrols to escort and join them in their fights (and their Lords/Ladies patrols will escort them as well).  This makes for a really giant force working together to conquer.

So, be careful with huge empires unless you want a lot of troops coming to take over your settlement heh.
fixes
other stuff

Adding a custom troop tree
I did as people were asking and made a shell troop called "trp_custom_recruit" and "trp_f_custom_troop" (for female recruit).  So you can use the troop editor to make troops as well now, simply edit the "trp_custom_recruit" and female version to be your base troop in your tree, and make upgrades from it.  Then ingame simply choose "Manage Faction" then "Choose Culture" and then "Custom Culture" and then the base recruit your faction uses will be the custom troop.

0.67 is not savegame compatible.