I think iCloud could be a whole lot more. Apple hyped it up so bad that I was disappointed when I actually got to use it. Maybe it's because my iPhone is my only Apple product so I don't get to use the full ecosystem. The only thing I really find useful is the overnight backups.
Thumbs up for...
Backups
Address Book
Thumbs down for...
Photo Stream
iTunes Match
iWork
The question "Do you use iCloud?" is so broad to me that it doesn't even make sense. Anybody who has ever made an Apple purchase "uses" iCloud to the extent that you have the freedom to delete and then re-install music, apps, etc. through your Apple ID. That is a HUGE feature.
I think the name of "iCloud" is what throws a lot of people off. A "cloud" service can be anything from complete mirroring of devices to a online storage system or web portal. Apple gives you 5 GB of iCloud storage, but as is often the case with Apple, it's not like you have the freedom to do with that space what you will. I think the rumored changes to Photo Stream were the first acknowledgment that they might reverse course and give you some power over what gets retained in the cloud and what doesn't.
I haven't tried to use "Backups" yet, but for Contacts and Calendar alone, iCloud is AWESOME. Having full access to my wife's calendar (and vice versa) has completely changed our household.
Photo Stream is a failure, but I think if they just allow you to delete photos from it, a lot of people will appreciate it. They really should do a better job integrating it with other services, however. If these photos are being shared on other devices, then it should be easier to just log onto the iCloud website and view them on PC so they can be sent to other services, emailed, etc.
It's possible to do all of these things with separate apps already. There are shopping list apps that work like a "cloud" service and can be updated from multiple devices. Google Music is a free "cloud" music service that allows you to access your entire iTunes collection from an internet stream, without using any precious memory space on your device. I think iTunes Match is largely a failure, but I understand what they were trying to do with it. To me, there are just better alternatives out there.
Haven't done too much with iWork yet, but it LOOKS impressive. I think the issue, again, is that a lot of people still have PC's instead of Macs, and if you have iCloud service that deals with Word Documents, Photos, etc., those are things that people want to be able to access freely with their home computer. iCloud allows you to do that, but it could be a lot better.