Here's a quick summary:
1. Bootcamp
What it is: A dual-boot solution that give Windows full control of your Mac
Pros: Photoshop will run at full speed
Cons1: You need to reboot
Cons2: You need to install the whole Windows operating system
2. Parallels
What it is: A virtual machine solution, where Windows runs inside the Parallels virtual machine on top of Mac OS X
Pros1: Looks cool, seems convenient
Pros2: Except for Bootcamp, the arguably the fastest Mac virtual machine solution to date
Pros3: Can run Windows apps in a window mode side by side with mac apps without having to see the whole Windows desktop
Cons1: Photoshop will run slower, actually much slower due to virtualization
Cons2: You need to install the whole Windows operating system
3. VMWare
What it is: A virtual machine solution, where Windows runs inside the VMWare virtual machine on top of Mac OS X
Pros1: Like Parallels, you don't need to reboot
Pros2: I would argue that VMWare's greatest value is for corporate users, and not individuals. The use case is that, your company can have "pre-packaged" and "pre-tuned" VMWare images for different purposes. There are many corporate applications (e.g., SAP, Oracle, Peoplesoft etc) that are quite daunting for the mere mortal to configure and need far too many bits and pieces to be installed. So the neighborly corporate IT dept will "pre-package" whatever is needed in a VMWare image. And all you have to do is to load it and use it. In short, you can have the EXACT work environment sitting on top of your Mac or whatever machine you're using at home... a very powerful proposition... erm, not to you, but for your bosses, haha!
Cons: Same as Parallels, but a little slower
Hope this serves for a sobering Sunday morning read