Multiple Apple IDs on one iMac
Yes, if you have separate user accounts (ie. there are two login options when you boot your machine), then each account can be associated with its own Apple ID for iCloud.

All preferences, documents and other customizations are individual to each user account. By default, Applications are shared (they get installed to /Applications), but you can install an application for just one user by installing it to the Applications directory within the users home directory.