The Windows Azure AppFabric Caching is a very powerful and easy-to-use mechanims that can speed up your applications and enhance performance and user experience.
It's Windows Server Cache but different
The Azure Caching contains a subset of features from the Server Appfabric. Developing for both requires the Microsoft.ApplicationServer.Caching namespace. You can use the same API but with some differences (isn't that a shame! because without this it would be a matter of deployment instead of an architectural decision). Differences are e.g. anything with regions, notifications and tags are not available (yet). The maximum size for a serialized object in Azure Cache is 8Mb. Furthermore, since it's cloud you don't manage or influence the cache directly So if you want to develop multiplatform for both azure & onpremise you need to differentiate on these issues and design for it. Always design for missing items in cache since you are not in charge (but the Azure Overlord is) and items might be gone for one reason or another especially in cases when you go beyound your cache limit.
Expiration of Windows Azure cache is not default behaviour so least used items are ousted when cache reaches it's limit. Remember that you can add items with a expiration date/time to overrule this default behaviour.
cache.Add(key, data, TimeSpan.FromHours(1));
It's obvious that this statement will cause my "data" to expire after one hour.
Keep in mind that using Windows Azure Caching you have caching on the tap and keeps you away from plumbing your own cache. Keeps you focused on the application itself while you just 'enable' caching in Azure and start using it. Fast access, massive scalability especially compared to SQL (Azure), one layer that provices cache access and a very easy, understable pricing structure.
A good alternative even for onpremise applications!