For basic photo editing with Photoshop, the Mini is usually more than sufficient.
As for the cheapness of the PC, you get what you pay for. Generally speaking virus protection and spyware are a much larger concern for PCs than for Macs.
Apple uses its own firmware for holding the operating system to a specific range of Macs. Macs older than a certain date can't upgrade past a certain operating system, and Macs newer than a Mac operating system can't get the older Mac operating system installed. This allows for a tighter integration of software and hardware than normally found on PCs. Macs will remarkably allow you to install any PC operating system these days though and run it like a PC.
Most of the time, though the PC data formats are usable on Mac operating system based software.
The MacBook is an excellent notebook and the MacBook Pro in my humble opinion is a better deal than the MacBook, because Firewire offers you up to 64 ports at up to 6 times the speed of USB. USB's real speed is only about 150 Mbps, and slower when multiple devices are on the same bus. Firewire 800 is a true 800 Mbps.
There are used and refurbished MacBooks from prior to October 2009 that have Firewire 400 on them. They are white. And that's true 400 Mbps.
See my FAQ*:
http://www.macmaps.com/usedrefurbished.html
for more details on how to get them and not get ripped off.
- * Links to my pages may give me compensation.