J.E. Sawyer, the Fallout: New Vegas lead designer, has released a bug fixing and difficulty tweaking mod for the game titled simply "JSawyer". It is a personal mod intended for those willing to experience a harder, more challenging Fallout: New Vegas. It also includes several technical fixes and tweaks (particularly to the Karma system), that were not included in previous patches.

Here's some of his answers to questions about the mod from his Formspring:

Why can't you just add your changes to the game in an official patch?

The short technical reason is ".esm inter-dependencies" and "load order errors". Sorry.

In addition to technical reasons, some of the mechanics changes make the game significantly more difficult (base health / stim changes) or at least more of a hassle (carry weight, stims having weight, H2O/SLP/FOD rate increase). I'd rather have people opt-in to those changes than make them the default in a patch.

Finally, the game's over. The ship has sailed. No one is working on it anymore. No testers, nothing. This mod is just me working in my free time. If I horribly botch something, you can just un-check the mod and go on your way.

Do you plan to reintroduce the armored vault 21 jumpsuit in your mod? If so, would it be by crafting or found?

Yes. It is for sale in Sarah's store at Vault 21. Both it and the Armored Vault 13 Jumpsuit now use the RepairVaultSuit list and have 200 CND. The Armored Vault 21 Jumpsuit grants 12 DT, +1 LK, and costs 2000 caps.

Will your mod add any removed/unfinished quests?

No.

You can find the full list of changes in the mod in the wiki, while the mod itself can be downloaded here.