The only work I've ever subbed-out is graphic design (know your weaknesses!). Development work I've always done myself and I've been lucky enough that - even in the busiest of time - I've been able to cope single-handedly.
Subcontracting dev work out is something I've purposely tried to avoid. Partly because I don't trust others and don't want to be a manager, but also because I think my customers come to *me* to do the work.
Not subbing work out is the reason the chart I posted above is now at the ceiling of how much a one man company can feasibly earn.