Welcome to the patchnotes thread. I'll keep this post updated with all the patchnotes, whenever a new patch comes along. Feel free to comment, if you notice something missing.
Up top are the base stats of what changes were applied. Below, a discussion of the reasons for the change.

V5: Bugfixing the Shoshone again (January 15th, 2014)
Some changes to the Shoshone pathfinder:
- Returned recruitment cost to default. For whatever reason, changing the recruitment costs was what made it stop being the default starting unit the Shoshone get instead of a warrior.
- Reduced base strength to 6, compensating for the cheaper recruitment cost.

V4: The Big New Year Release (January 3rd, 2014)
Balance is the thing:
- Removed Deadeye promotion (1 Extra attack) from Special Forces
- Reduced Ranged damage upgrade modifier from +200% to +100%
- Reduced Ranged damage against Cities by 150% (to compensate for the +100%, the tooltip lies intentionally to prevent popped veins and strokes)
- Reduced the Extra Range from Sniper 1 Promotion (but doubled its ranged damage boost)
- Changed the tech prerequisite of Explorers from Compass to navigation
- Increased cost of recruitment for Scout and Explorer
- Vastly increased costs to buy Rangers and Special Forces (So it's insanely expensive to just pop a high defense unit whenever you need it)
- Increased Maintenance Gold cost of Ranger and Special Forces
Bugfixes and typos
- Fixed Goodie Hut Promotion bug for Scouts, where they would get promoted to Settler
- Fixed Goodie Hut Promotion bug for Pathfinder, where the upgrade unit option would not show.
- Fixed more typos than I ever realized I had made
- Fixed some behind-the-scenes stuff to improve some compatibilities with other mods
Information & Language
- Improved Tooltips
- Improved Civpedia entries
- Full German localization

V3: Grand Expanse Update
Finally the Shoshones get a fair deal: Pathfinder receives the same upgrade as the scout does. And Shoshone Scouts of all eras are linguists by nature, so you keep your "pick-your-goody" ability throughout the eras.

V2: Compatibility Update
No content changes, but fixed the bug that prevented the Explorer from loading in Brave New World.

V1: Alpha Release
No new unit graphics, just stealing icons, animations and unit-graphics from existing ones.


Patch 5: Shoshone again
One of the trademarks of playing Shoshone was starting with a Pathfinder. Patch 4 broke this by accident, since one of my balancing acts was increasing the recruitment costs to the same level as a warrior. Having to undo that, I had to find another way to reach balance in this matter, so I reduced the base strength of the Pathfinder from 8 to 6. Still better than the Scout, it's a significant loss, factoring in all the insane boosts scouts get (and for which they pay with low base strength).
Still, they are significantly faster to produce, which will make swarming the regions with scouts easier for Shoshone. This makes this patch a combat power nerf, but a strategic buff for the Shoshone.

Patch 4: A matter of balance
Balance is not only important to Liadens (kudos to whoever caught the reference without looking it up), but also for a game to be enjoyable. An extremely powerful unit may be fun, just to go on a rampage some times, but in the long run, it removes challenge and diversity from the game. It gets boring. That said, several balancing acts were performed, each with a reason I consider significant enough:

Reduce Ranged damage / Drop one Extra Attack from SF
The SF was never meant to be a mainstay ranged combat unit, that replaces the main battle line. The incredible mobility and many utilities already makes it a great strategic unit, but if it can kill the main combatants in a single turn at a long range (in addition to all the other benefits), it's just too powerful.

Reduced damage against cities / Reduced range
Long range is fun, but having a longer range than most artillery (combined with massive mobility, the weakness of common artillery) was overkill. Not only could it easily duel an artillery unit (that costs strategic resources), it could also take on cities (not quite as effective as artillery, but fast enough). This meant the Ranger and SF could replace artillery, instead of supplement it. Not good.
3 Range is still plenty - better than modern ranged infantry can otherwise manage - and the high mobility allows hit-and-run. Not enough to slaughter a battle formation without giving it a chance, but enough to be a serious nuisance (which is within the scope of the unit).

Increased Maintenance / Buying cost
The (slightly) increased maintenance is to discourage using swarms of Rangers or SFs as powerful shield walls while artillery and aircraft deal with the attackers. That's a line of battle's purpose (Mechanized infantry, anybody?). The increased gold cost to buy them (in opposite to recruiting them with production) is to avoid using them as instant-ready shields (besides, Special Forces take ages to train, equip and deploy, so take your time and do it properly! ;) ).

Moving Explorer tech prereq from Compass to Navigation
I always compare a scout unit to its baseline infantry equivalent.
The Scout (5 x 2 = 10) is compared with Warrior (8) / Spearman (11)
The Explorer (10 x 3 = 30) is compared with the Rifleman (32)
The Ranger (15 x 4 = 60) is compared with the Infantry (70)
The Special Forces (20 x 5 = 100) is compared with the XCOM Squad (100)
I try to somewhat balance power, cost and time at which you have access to the unit. The Explorer was unlocked a full age before the rifleman, when the most powerful unit (and that some techs later) has an attack of 25 - and it's a ship. The Explorer will still be unlocked earlier than the Rifleman, but now they are only separated by one tech tier.

Something that may have confused: The Chosen Few
The Chosen Few promotion increases ranged attack power by 100%, but reduces damage against cities by 150% (to a net result of -50% against cities). This is not a major buff to ranged damage in general over previous versions! In previous versions, the "Big Muscles" promotions for Ranger and Special Forces had an undocumented +200% Ranged damage boost. Which was too much. I split them into separate Promotions so things make a bit more sense on the tooltips (and rolled in the City attack penalty, to prevent too excessive Promotion bloat. I know I failed that one, but all one can do is all one can do).