A few possible tricks & tips:
- Turn off PSN
- Turn off auto save
- Turn off background music
- Clear out old games + saves
- Don't overstrain save slots, use a max. of 5 or 6 slots
- Delete and reinstall game data (not your save games)
- Turn off radio especially in buggy areas and combat situations
- Conserve the use of energy weapons due to goo & ash pile glitch
- Be careful using VATS in heavy combat scenarios especially if lagging starts to occur
- Clear cache: start up the game, press and hold L2 + R2 + Square until you get to the title screen
- When entering a new area let the scenery load for a while until the flashing disc light stops
- Make sure your console is placed on a cool, clean ventilated spot
- When lagging occurs press XMB and wait a few seconds
These are a few measures that will reduce (not prevent or totally eliminate) this freezing issue.
When your save game reaches over 10 or 12Mb the lagging and freezing usually gets worse and worse, no matter what.
Hope it helps.. Cheers!