I'm currently comfortable in three operating systems, but then no one uses spectrums anymore.
can switch between both mac (tiger and leopard) and windows (most versions going back to 3.1) with few worries
a fair bit of swearing when windows falls over, had the PC 4 years, 8th install of windows, 5th PSU, 3rd hard drive, its also caught fire.
having had the warenty and tech support finish (given to me as part of disabled students allowance) its now a lot more reliable except for the recent windows failing to load.