Coming from experience switching folks from Exchange to Google Apps... be careful what you ask for.

I had a number of customers running Small Business Servers that had Exchange 2003 on them. With support running out, the need for better spam protection, amongst other things, we were deciding whether to upgrade Exchange or move to Google Apps, which at the time was free for customers under 50 accounts. I've also setup a few Google Apps accounts for users who have never had Exchange. Their experiences couldn't be any more different.

The migrated Exchange users for the most part were very unhappy. Scheduling, Calendars, Synching were big examples of things that worked completely different and or were missing. Outlook played a big part in this, as it is completely integrated with Exchange. Google Apps... well not so much. They make things work with Outlook, but as example, setting your Vacation Reminder requires a visit to the website rather than a simple setting in Outlook.

The users who never had Exchange, couldn't have been happier. It's all they knew. They had access to things like shared calendars, albeit not in Outlook, but at least they had it.

I realize you are not talking about moving to Google Apps, and I have not looked at any of the solutions you linked to above. I just know you could be going down a road of pain and heartbreak. Your users could very well hate whatever choice you make because they have already had Exchange.

Have you considered Microsoft's hosted Exchange / Office 365? I have no idea what the price difference would be for your situation, but for small offices, it's a near no brainer. Setup was very quick and easy. I have set it up for one of my smaller customers (as a live beta \:\) ) , and have to say it works great.