Your files, anywhere
You could also browse your files at your leisure in a coffee shop using such services' sync apps for your iPhone or Android handset. And, if all else fails, you can access your files using a web browser too. In other words, you’ve got access to all your important files on any digital device in any location that has Internet access. You can also let friends and colleagues in on the act too, as many services like Dropbox allow you to create ‘public’ folders for sharing files with other people.
Price can be an issue if you need more storage than the sync services provide for free. Dropbox, for instance, only provides 2GB of storage for free – which would be just about enough for my personal batch of work files – but the next step up is $10 (£6) per month for 50GB, or $20 (£13) for 100GB. Even so, its flexible and easy-to-use syncing features are really useful for people who frequently switch between multiple devices and locations when they’re working.
Review: Apple MobileMe iDisk
Apple’s MobileMe provides a wide range of online services, including synchronisation of email, contacts and calendar info across Macs and PCs, as well as iOS devices. However, its iDisk online storage feature is actually a relatively minor part of that overall suite of services, which means that MobileMe isn’t the best choice if you’re simply looking for low-cost online backup.
You can access your iDisk and other MobileMe services through a slick browser interface, or via the iDisk app for the iPad, iPhone and iPod Touch. Needless to say, Apple doesn’t acknowledge the existence of any other mobile devices. Macs, but not PCs, have desktop access to the iDisk.
The storage space on your iDisk can be used for backing-up files, but it doesn’t allow you to sync ordinary files and documents that you might need for work. That means that it’s more expensive than Carbonite or Mozy and less flexible than Dropbox. I found it a bit slow, too.
Even if you're a MobileMe subscriber for the data synchronisation or other features, you'll probably need a second service for file syncing.
Reg Rating 60%
Free Storage None
Extra Storage 20GB: £60 per annum. 40GB: £90 per annum. 60GB: £120 per annum
More info Apple
Next page: Sky high
Do these 'free' services help themselves to a lifetime worldwide licence to use your data?
Can you be sure data you've deleted is gone?
Is my data encrypted?
What assurances do you have over availability of your data?
If the company goes bust does the liquidator inherit my data?
If the company goes bust can I still get my data?
Where do the back ups go?
Is it legal for my data?
Before you upload your office data to those services have you considered the impact on your companies policies and legal requirements?
Are you transferring personal data out of the EEA and therefore breaking the DPA?
There are so many questions you have to know the answers to before you use these services. It's not simply a matter of how much is it and how easily can I spread my data.
from a home user's perspective...
Will amazon/apple/microsoft/et al be trawling through my files to try and sell me things?
Will I find my university thesis/latest novel in progress/etc available via Amazon if i search?
Will i find my holiday photo's used in Microsoft's latest marketing campaign?
whilst other people getting at your data is one thing, how trustworthy are the people you are handing it to, and what access are you granting them in exchange for this "free" storage?
I agree, there is a lot of questions that *everyone* should be asking of on-line providers, and I guess the above list covers the key ones. In fact, the simplest of all is this:
Do I have the encryption key, and it is not known to the storage host?
For most other factors, where the data is held, what happens if they are bought/liquidated, etc, they become less important as they cannot DO anything with my data as they don't get it plain-text.
OK, you have to ask what happens if it vanishes, but again you must look at the 'cloud' as a good HDD, not as a complete solution. You should have 2 copies of your data no matter what! 
And I know the arguments about de-dupe, but surely you could have a user-side client encryption that is block de-dupe friendly by encrypting blocks of the same size (4kB, 64kB?) with the same key-based pattern so they still de-dupe even if the plain text is unknown?