No, I did not reboot after completing the installation. As an application with out device drivers or system files, I did not think a reboot was necessary.
I am getting comfortable with SPP 3.5, it has a nice full screen slide show, recognizes more than X3F, JPG, and TIF files and I can open a directory with the thumb nail view containing a AVI video, double click on it and SPP will start up Irfanview to load and play the video. You even have a choice under the preferences to specify the default or another movie player.
For me, opening a X3F file still takes a bit of time. At least the progress bar gives an idea how far along it is. I never played much with the White Balance in SPP 2.5, especially when I found that changes are immediately saved to the original X3F file, but I've noticed that SPP3.5 has a monochrome which, in combination with the Color Adjustment, can create some interesting tinted B&W effects.
Since my initial instability has cleared up, it looks pretty good.