What are the advantages/disadvantages of the various cloud storage solutions for assets? When setting up a new assets source, Craft allows you to natively connect to one of these cloud storage solutions (assuming you're using the Craft Pro edition):


Amazon S3
Google Cloud Storage
Rackspace Cloud Files


I know that the answer may be subjective, but want to hear pros &amp; cons from people who have tried any of these. I'm working on a project which will require one of these solutions, and I greatly value the opinions of this community.
Allright, I'll bite. First, I'll get the cost argument out of the way, then I'll cover each type with their specifics.

Costs


Amazon S3: USD 0.03 per GB (up to 1TB, where the price drops as you store more and more data)
Rackspace: USD 0.12 per GB (up to 1TB, where the price drops)
Google Cloud Storage: USD 0.026 per GB (No price reduction for large amounts)


In conclusion - pricing will not be a deciding factor, as the difference, while having a rather noticeable amplitutde, only matter when storing such an absurd amount of data, that the price is the least of your problems.

S3 Specifics


Superb integration with AWS. If you're hosting there, then your choice has been made.
CDN - Amazon Cloud Front is super-easy to set up and is a breeze to use.
Different types of storages available. 

Regular
Reduced Redundancy Storage - cheaper, however Amazon guarantees "only" 99.99% durability of data
Glacier - super-cheap storage for archiving. Super long data recovery, though. I'm talking 3 to 5 hours. Also, as Matt Stein pointed out, in some cases, the data retrieval could get super-expensive. (more info, expensive retrieval case)

Supports object versioning (more info)
Cache headers - you can set up cache duration per Assets source for files uploaded to the source via Assets


Rackspace Specifics


CDN built right in - no set-up necessary.
CDN comes at a cost - you can purge only up to 25 files from the CDN per day, so be careful with frequent file changes. (blog post)
Supports object versioning (blog post)


Google Cloud Storage Specifics


Cheapest of them all.
Offers Durable Reduced Availability storage. Cheaper, but stores data on further servers, so the data recovery time is slightly longer.
Cache headers - you can set up cache duration per Assets source for files uploaded to the source via Assets
According to google, CDN is built in at no extra cost. (Google groups post))
Supports object versioning (more info)


Overview

I am biased, I'll admit that, but I've had nothing but joy working with Amazon S3, a lot of frustration working with Rackspace and mixed feelings when it comes to Google. For Google it's mainly of their unbelievably clunky UI, but that might be just me.