From all the sources available on the web talking about the successes and failures of Google Apps deployments, it's clear that the main pain points are with those tools where someone will use them not just a few times a day, but several times an hour, if not incestantly.
If you haven't already, have a read of this Article here by Shane O'Neill over at InfoWorld. In it, he talks of several companies that tried Google Apps and all are moving on to the Microsoft Cloud Applications. I thought it would be handy to summarise their complaints here:
Problems with the way Gmail works
Threaded messages and the way meeting invites works was quoted as being a problem for the first company:
In Gmail, a frequent irritation for Harris was that there is no way to resend a message (as opposed to forwarding), which can come in handy if you have a regular email that you send out each month. This is something that you can do in Outlook.
In Outlook Connector, a problem for Aisle 7's users was with meeting requests. One example: If Aisle 7 users included an attachment in the meeting request, the invitees would not see the attachment nor could they accept the meeting request, and the organizer wouldn't know there was a problem.
Also, if users received a meeting request in Gmail using Google Apps that was sent using Outlook, they could see the date, time, and invitees, but they could not see notes written in the body of the invite by the organizer.
It is true that the threaded messages view are a different way of going about things. The key to overcoming this is to understand that Google has a different viewpoint in mind for its email. For MS Outlook, the ability to quickly and easily see linkages between mails, and also to search all mails has, it seems to me, been something that was a little bit of an afterthought. Any system which needs to either keep messages on a server (with limited space), or download to your local machine, isn't thinking through the need to see context in messages or the need to find them quickly. For Gmail, context is rarely lost - as you have the entire set of messages available, in an I said, he said format.
Outlook Connector?
There has been quite some discontent with Google about their Outlook Connector software, which enables outlook to work 'normally' with GMail in the background. Whilst I agree that having an incomplete, buggy and failure-prone piece of software isn't good, I would also challenge an organisation thinking about this to ignore Outlook Connector. If you're contemplating the cloud for your business, then use it. Users need to know and learn that Google Apps, or any other provider is different. Use the Web Interface.
In my opinion, email and Outlook is a bit like learning to walk - you did it once, but now its second nature. Replacing that second nature with a new way of walking or a new way of emailing is one of the most difficult tasks- but it can be done. I would approach this change as the most sensitive and delicate you're ever likely to put your organisation through. Yeah its just like using webmail, like you do at home, but changing the way you walk is damn difficult. Ask a physiotherapist.
Poor change management
All these stories smack of poor change management. There's plenty of talk about what users didn't like, couldn't or wouldn't do, but no talk about managing these users, managing their expectations, and taking them on a journey of change. It won't guarantee success, but engaging with someone who can identify change, indentify user needs and establish a mitigation plan is probably a first step towards success. Get involved at the conception stage, throughout the planning phase and ensure that change management is a deciding factor in how your roll-out works. It won't guarantee success, but it might make your users happier and mean that their dependency on MS Outlook isn't holding your organisation to ransome.