There are many variables involved in how much static voltage triboelectrification creates, including the materials involved and the humidity. Low humidity causes static shocks with more kick. But for PC upgrades, the important thing to remember is that while a static shock must be 3500 to 4000 volts before you can feel it, it's the voltage below that level that is common, and insidious. It's entirely possible that you'll open up your PC, plug in an add-in card or some RAM, never have any sensation of static, and still have zapped the electronics. That's because the integrated circuits can be damaged or destroyed by static voltages as low as 400 volts.