[imglorp]

The hard part is most houses do not contain a single plumb, true, and square room. Walls do weird things, especially where they meet floors and ceilings. Floors are hard to get flat. Etc. I'd say once you resolve all this and get your rail level and parallel to the floor, yes, then throwing up the cabinets is the easiest part. After that, you probably want to learn how to do some molding to trim them in.

[bastawhiz]

Having someone else install your IKEA cabinets for you probably won't help with the quality of the installation if your house is a bit wiggly around the edges.

[shostack]

Perhaps not, but the hope is someone who installs this stuff for a living has encountered these situations enough to know how to handle them, whereas the average person who might try to install this on their own is likely encountering that for the first time.