This is an FAQ long overdue, but the answer is still the same. If it takes forever for the lot to load (once you're already in the neighborhood), chances are a recolor or a new object mesh or a hack snuck in with that lot (or custom content you recently downloaded) that was badly made or incompatible. Make sure you read all the disclaimers that come with the download before installing. Make sure you have all the necessary components.

If you ever find yourself in this predicament, take this as a suggestion and start organizing your downloads and follow this guide.

If you put everything you've downloaded into your Downloads folder, the best thing to do is to move the folder to your Desktop and then start the game up again. Will your lot load now? More than likely you should no longer have any problems and that only tells you that the problem stemmed from something that you downloaded. Now you'll need to go through your Downloads folder and find the culprit.

Create an empty Downloads folder in C:\Documents and Settings\username\My Documents\EA Games\The Sims 2 and then reinstall the CEP files. Then start moving your files back (from the Downloads folder on your Desktop) a handful at a time. Restart your game and test loading your lot. With the next batch that you move, if the lot freezes while loading, then you know the problem child is in that batch.

Note #1:
If you can remember the date of last time you had no problems loading that particular lot, then sort your Downloads folder by modified date and take out all the ones that you put in there after that date. That might help narrow down your search (especially if you have tens of thousands of downloaded files).

Note #2:
Use Clean Installer when installing lots. The current Maxis installer grabs anything and everything when packaging lots so you really don't know what you're getting unless the creator is mindful to check the .sims2pack before sharing it with the world. This is sooooo important and can't be stressed any further. You can find Clean Installer here: http://sims2pack.modthesims2.com