A handy feature of Lucidchart is that it integrates with Google Drive, so your diagrams will show up in your Drive folder with all of your other files. Similar to Google Docs, Spreadsheets, and Presentations, Lucidchart also provides real-time collaboration between users in the same document. *Note - I did discover that both users need to activate Lucidchart by going to Drive -> More -> Lucidchart before a document can be shared and edited by both people.
If you are interested in checking out Lucidchart simply look for the application near Sliderocket under the More tab in Google Drive. The first time you launch the application you will be taken through series of set-up screens that will allow Lucidchart to access Google Drive.
Below is a tutorial video of the Lucidchart Editor which does a pretty good job explaining the application's key features. If you would like more tutorials Lucidchart also has a series of instructional resources from creating a new document to using the real-time collaboration features on their website.
Please let me know if you have any questions.
2/5/13 Follow Up
After creating this initial post and working some of our teachers I discovered that Lucidchart has a ton of great education templates. This video will show you how to access those.