Boot-Time Results
Testing boot times can be tricky, because it's hard to know exactly when all background processes and services have loaded into memory--even if you get to the Windows desktop quickly, your PC might still be loading tasks, so it isn't fully responsive yet. William Wang in the PCWorld Labs tested boot times by setting each PC to open a Notepad document on startup, and stopping the stopwatch when he saw it appear on screen. He tested each setup ten times. (Click the chart below to see it at full size.)
Each utility managed to speed startup slightly, though typically by no more than a few seconds. Oddly, System Mechanic 10 caused a negligible increase in startup time in the Dell D520 and the Toshiba M645-S4055, but the difference fell within the margin of error. The Lenovo ThinkPad Edge, meanwhile, enjoyed faster boot times across the board; CCleaner came in first with a 10-second improvement (19 percent faster), followed by System Mechanic 10 (9 seconds), WinOptimizer 7 (6 seconds), and System Speedup (4 seconds).
Net-Connection Speed Boost?
While all of the utilities made claims about improving overall performance, System Mechanic 10 also touted its NetBooster and Internet Connection Repair tools: "By adjusting the settings that affect network and Internet connection speeds, NetBooster fine-tunes your configurations so that more data can be transferred."
Unfortunately, no sophisticated Windows magic seems to be going on here. The optimal MTU for your PC depends on whether you're using an always-on Internet connection (such as standard DSL/cable), a PPPoE (PPP over Ethernet) broadband connection (if you have DSL/cable service that requires you to log in at every boot-up, you're probably using PPPoE), or a 56-kbps dial-up connection. System Mechanic simply asks you which type of connection you have during the setup process, and adjusts the MTU accordingly (1500 for a standard always-on connection, 1492 for PPPoE, or 576 for dial-up). You don't need System Mechanic to do this task, though: The oldie-but-goodie Dr. TCP will help you change your MTU for free.
Our Advice
The reality is a bit different: You might feel better after running a utility--but judging from our testing, your PC's overall performance is unlikely to change much. Instead of investing in a cleanup utility, uninstall old programs for a short-term speed boost, and save your cash for a hardware upgrade.