I have some great news. I received this PM from BellaClo, who I ask about patches. She's been a great help in the past. She got some of this info from a mod site, so I've edited it out from her PM.
This information is correct for me.
Ok, I've done a bit of reading. What I write below is strictly theoretical on my part since I haven't even tried to patch myself so far.
Latest patch level for PC is: 1.22.9 for basegame, 2.17.2 for WA, 4.10.1 for AMB, 6.5.1 for LN.
(other patches have been released for Mac only, they are 2.16.6, 4.9.5, 6.4.4. Don't get confused with them)
You don't have Generations yet, right?
And you have only disk versions installed, no digital download?
And your latest EP or SP installed is still Late Night?
You should only need to patch base game and LN. Here is what's written in the stickied thread on official forum: (find thread here)
IMPORTANT
The way the game updates work is that only the base game and the most recently released and installed title need to be updated - the products in between are ignored as far as version numbers are concerned. You can manually update the other products in between if desired, but this is not necessary.
All expansion and stuff packs released after World Adventures now come in only two game regions:
Region 1 - Disc Version (regardless of geographic location)
Region 7 - Digital Download Version (regardless of geographic location)
I can only find cumulative Super Patches to match the latest patch level. The name "Super Patch" seems especially well chosen for base game patch because this mamoth weights a nice 644Mb. Hope you have a good bandwith!
Here are the links (they come frome EA forum, no stress 
):
Base game to 1.22.9, region '1' (disk version, 644 mb): http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims3/patches/TS3_1.22.9.0110xx_update.exe
Late night to 6.5.1, region '1' (disk version, 6,30 mb): http://akamai.cdn.ea.com/eadownloads/u/f/sims/sims3/patches/TS3EP03_6.5.1.011031_Update.exe
If you also want to patch your other EP (WA and Ambitions), the links are on the thread I quoted from here above.
Then, it seems the .exe used to load the game directly (skipping the launcher) has changed. Here is what I found on [removed]:
As mentioned above, the Standard Operating Procedure (SOP) EA has established since patch 1.5 for WA is that each base game + last-released-installed pack, need to be updated in turn. However, most of us had patched all installed packs in the middle as well, as that procedure appears to reduce crashing and other weird issues. So, [Name removed] staffs' advice has always been to keep all your games on the same patch level. This is because the patched files are stored in the last-released-installed pack's folders as well as each pack's own folders.
In 1.22 however, the patched files are stored in base game's folders and it does appear that games with unpatched packs can be started just fine even if one does not have the last-released pack that goes with that patch version (eg Base Game on 1.22 minus Generations on 8.0). But reports I've read have been mixed with myriad of stories. I believe this is true if you start the game via TS3W.exe in /Game/Bin or via Launcher, and the unsuccessful reports are from those who start their game from TS3?P0#.exe. Still, time will tell...
So, if you only start your game with the Launcher, there should be no problem for you. Your Launcher.exe will have been updated with Late Night's patch.
If you have a shortcut on your desktop to launch the game directly, you'll need to replace it, as far as I understand.
And last but not least, CAW has been updated too. Another big download :-)
Hope this will help you and you'll be able to patch and play.
EDIT: I'm downloading this patch after hearing about this. It's the second time downloading it; my USB ran out of space the first time. I cleared some stuff out and I'm trying again. I'll totally empty it if it doesn't work THIS time.
EDIT 2: If you are reading this and want to download this patch, there's one thing you should do before you even think about downloading. Back up your whole "The Sims 3" folder.
EDIT 3: The LN patch downloaded in less than 30 seconds. The other one downloaded in 10 minutes. I think. I'll apply the LN patch then get back to everyone on how it's going.
EDIT 4: So far, so good. I'm loading the Marsden Unofficial Dynasty. Nothing bad has happened *touch wood*.
EDIT 5: I can confirm the above patches work.
