If your system is slight on RAM, it may become bogged down if a large system cache uses memory unnecessarily. If that's the case, O&O CleverCache Professional ($30, 30-day free trial) may help speed up your system, freeing up that RAM for use by memory-hungry applications.
This is a set-and-forget application. Run O&O CleverCache, and it automatically monitors your PC use and system cache. When it detects that your cache holds data without reason, CleverCache frees the data, giving you more RAM to run your programs.
O&O CleverCache has modules for reporting on system information, including details about your hardware and operating system configuration. It also monitors and graphs your processor use, RAM use, system cache use, and hard disk use.
As I used the program, it generally reported freeing between 300MB and 400MB of memory from my system cache. I could not see a noticeable performance increase as a result, though, because I have 2GB of RAM on the system. It's possible that on systems with less RAM--or more demanding software--a performance increase would be more noticeable. So if you've got a sluggish PC, and think an unnecessarily large cache may be the cause of the problem, download the O&O CleverCache Professional and take advantage of the free trial. If you don't notice any performance increase, you won't lose anything but a little time, because it's also easy to uninstall.