Many other Wycliffe organisations in the Wycliffe Global Alliance have moved to Google Apps, and we decided to join them. Here are my experiences:
Google Apps is free for UK charities, which is an attractive price. However it doesn't mean that it doesn't cost in time. Doing the migrations, plus user training and support all take non-finite amounts of time.
As well as the familiar Google tools, such as Gmail, Calendar and drive/documents, you also get the management interface so you can create and suspend users, turn services on and off and generally manage the stuff.
I've been disappointed with a number of problems that we've had. They are mostly to do with the migration. If you read the forums you find that some of them have been around for a few years with no sign of them being fixed. For example, when you view email that's been migrated using IMAP from Outlook all the dates on the emails are set to the same value. This is because the migration process sets the received date to the migration date. There is a workaround - display the sent date. However, it's a bug - fix it already Google.
There are some Outlook features that are lost when email is synced back to Gmail, but I'm not entirely surprised that Google won't implement features across the board just because Outlook uses them. More information here.
The standard package doesn't include backup so you may want to purchase Google Vault just in case Google loses your email.
If your users already have Google accounts then it copes quite well with multiple accounts in the browser. There are a couple of exceptions - Drive and Blogger require you to log out of all accounts and log into a single one. It's not a surprise that Blogger doesn't do that, as it's a pretty dormant product, but Drive seems like a key part of the offering. Maybe it's being worked on.
On the plus side you do get other Google Apps features, like Drive and Hangouts which are of corporate use. Overall the experience is positive, but if you do decide to switch then allow plenty of time for migration.
Update: I found information about future updates on the Google Apps release calendar and linked newsletters. It looks like there's a fairly healthy amount of work being done on improving Google apps, if not the migration tools.