One of the most exciting features of the Spring 11 release is the General Availability of the REST API. The simplicitly of the REST protocol has helped make it the de facto lingua franca for Web 2.0/Cloud 2 applications (i.e. those that are inherently social and/or mobile in nature). The combination of Android applications and the Force.com REST API should therefore be like Sonny and Cher (that's right – I just made the first ever Cher reference in a Force.com blog).
For Force.com developers looking to develop Android applications that access Force.com data, the Force.com Toolkit for Android is still the first and best option. However the toolkit uses the SOAP Web Services API under the covers and if you'd rather use the REST API directly from your Android app, here's an article that might interst you – http://wiki.developerforce.com/index.php/Building_Android_Applications_with_the_Force.com_REST_API.
The article walks thru a simple Android application that uses a combination of OAuth 2 and the REST API to perform basic CRUD operations on Force.com data. Though the article is specific to Android it does have basic usages patterns for the REST API that should be helpful for any developer interested in the API.
Now I'll get back to finding new ways for dating myself in blog posts.