uC-controlled high-side switch
The 2N3906 power switch looks OK as far as circuit topology is concerned. The 2N3906 is rated for a maximum of 200mA and as long as your total load on the regulator is less than that they you should be good to go. If you need a larger load current than say 150mA or so then I would recommend that you find another PNP transistor with a higher current rating. 

As designed right now the base current you pull from the PNP transistor is around 1mA. Considering that the worst case current gain of a 2N3906 is 30 you may want to consider changing the R10 to a lower value to increase the PNP base current up to the 8 mA level so that the PNP can fully saturate when the rated current is drawn.