Usually only the disk is really limited. Bandwidth may be limited by using devices with something similar to ALTQ, you only get a certain amount of bandwidth. Your datalimit isn't always limited but you usually have to pay when you go over your limit. This can be gathered from network statistics. Most of the time the throttling and accounting is done with specialized hardware.
Disks can be limited in a variety of ways depending on what the provider is using. You could use quotas or simply provide a fixed size virtual disk.
