If you feel like your Mac is slowing down, you can defragment - I know all about HFS's built in defragmenting for files smaller than 20MB, but I work with large pictures (40MB+), lossless audio (40-50MB/track), and gigantic video files (3-17GB/file). My drives (external and internal) were completely fragmented. Even though my ML installation was only a few weeks old, it was starting to feel sluggish when starting applications for the first time. Instead of clearing caches, which actually decreases performance, I used an old purchase of Disk Genius 3 to defragment my external HDD and my internal HDD. Surprise! Now reading and writing video files is far faster and has less latency. Applications open more quickly. Everything is faster. As a side note, it appears that HFS's built in defragmenting functions only defragment files, not move them into contiguous blocks - another detriment to performance. Disk Genius didn't find much fragmentation, but it did show that blocks of contiguous files were strewn across my HDD. Give it a try! WARNING: DON'T DEFRAGMENT WITH AN SSD - IT WILL DESTROY YOUR PERFORMANCE. OS X WILL USE TRIM AND HARDWARE BASED GARBAGE COLLECTION WITH APPLE SSDS, AND YOU CAN FORCE ENABLE IT HERE.