After an install built on forcepae the output of lshw or similar shows a CPU description which contains PAE, for example
product: Intel(R) Pentium(R) M processor 1500MHz
vendor: Intel Corp.
physical id: 1
bus info: cpu@0
width: 32 bits
capabilities: fpu fpu_exception wp vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 tm pbe bts est tm2 cpufreq
This might lead to incorrect statements like 'see, I already had PAE, so why did you want me to add the boot option?'
Just for stating the obvious, the PAE flag is not output from the processor itself, it comes from a software modification of the output. When helping beginners we might need to explain this more than once.