Last week, I listed my Top 5 Force.com Summer '12 Features, but there are several other features that I think are worth mentioning, including some non-development enhancements...
Salesforce Touch Beta
Other than the marketing videos, I haven't seen this HTML5 site in action so I am not sure how good it is. I assume that it is better than the current mobile options that Salesforce provides, so I am looking forward to checking it out. The web version of Touch will be available in all orgs by June 8. and the Touch App will be available from the Apple App Store later this summer. More detail here.
Single View State is GA
All forms are now merged into a single view state. This enhancement is very important if you include several custom components in Visualforce pages. Until now, each apex:form tag translated into its own view state, which increases the data sent to the client and reduces performance. More detail here.
Chatter Messenger is GA
As an SFDC consultant, I do a lot of my work remotely, so I use Skype A LOT for chat, voice and video conferencing. I can see how Chatter Messenger could replace my Skype usage in some cases because I am already in Salesforce all the time (although I often switch between orgs). For mid to large organizations, I see it as a great plus as users can get answers without getting up, which always increases productivity. With that said, I have to say that I don't like the location of the messenger tab - I think it should be moved to the header because it hides some of the data at the bottom, which is not great. More detail here.
Re-parenting of Master-Detail Fields
I never understood why this behavior was not the default to begin with, but thankfully, you can now specify if a master-detail field can support re-parenting. I needed that option several times in the past, so I am glad it is available now. More detail here.