60GB free out of how much?
The person who asked "60GB free on how big a disk?" is spot on.
All modern filesystems include mechanisms for avoiding defragmentation and all can suffer from fragmentation, but overfull disks are both a cause of fragmentation and a problem in their own right.
As a general rule you can avoid fragmentation and see much better performance if you keep your disks less than 60%-70% full and ideally keep them only 1/2 full. While that seems terribly wasteful, it has always been the case and it's also worth remembering that disk is very cheap now.
As disks get fuller all filesystems slow down and when you get over 90% full they get really slow. But fragmentation also increases as the disk gets fuller as there is less and less likelihood that an new block will be allocated in contiguous space and more likely that it will be allocated elsewhere.
Fragmentation is also more complex than whether the file is just fragmented, but also a question of how many extents are used, their spacing on the disk, the number of head movements, distance of head movement and so on, it all gets very complicated. There's a fella called Amit Singh who has written all about it if you really want the nuts and bolts.
I'd also have to disagree with people who have criticised NTFS for suffering more fragmentation and being messy. It's not really more or less likely to get fragmented, it all depends what you're doing with it, the type of files you store and how they change over time. NTFS is actually a very good and very elegant filesystem. There's some things it does better than HFS+ and some things that aren't as good. As ever, it's horses for courses.
Another point that several people have made is that SSDs overcome this problem, which is absolutely true. They still suffer from fragmentation, but as random reads on an SSD are barely any slower than sequential ones, then it makes not difference to the performance as perceived by you. The other beauty with an SSD is that you can fill it right up and it won't get a lot slower.
So, the summarised answer:
1. Get an SSD and use it to store your frequently accessed files (such as OS)
2. Buy a big spinning disk for your other files and keep it as empty as you can. If you can afford it, use 15K RPM SAS disks and put them in a RAID0+1 array for optimum performance
3. If all that is too expensive get rid of as much data as you possibly can or buy a bigger disk
