Memory usage

If you want to know how much the GC uses try:

GC.GetTotalMemory(true)

If you want to know what your process uses from Windows (VM Size column in TaskManager) try:

Process.GetCurrentProcess().PrivateMemorySize64

If you want to know what your process has in RAM (as opposed to in the pagefile) (Mem Usage column in TaskManager) try:

Process.GetCurrentProcess().WorkingSet64

See here for more explanation on the different sorts of memory.