Most designs and projects can benefit from abstract techniques as these techniques don’t belong to a particular style like grunge or retro, and they can add some vibrant colors, quality backgrounds, additional depth, texture or simple some shapes as eye candy.
Today’s link are several Abstract tutorials for Adobe Photoshop covering many different styles and techniques, for example creating the shapes via computer algorithms, drawing them with creativity and imagination or just following simple patterns that we had in our computer or stock images.
There are some aimed for experienced designers, but most of them are really easy to follow and very detailed step by step for anyone to start designing abstract shapes and backgrounds.
Link: Abstract Tutorials
Exactly, I would agree that these type of design is different from grunge or retro. It is somewhat a combination of grunge and retro (in my opinion).