I can't say how much support you should plan, most support problems are Outlook/Exchange related. There are many Outlook versions with or without service packs, same goes for Exchange.
Same version of Outlook may work prefect on Exchange X, but can fail after exchange upgrade. Our experience is that Outlook 2007 and 2010 are most stable versions, Outlook 2000, 2002 are very unstable. Outlook 2003 is somewhere between.
It also depends on how many records you will sync per user, example: 1000 users X 1000 records per user= 1 000 000 records!
In bigger Exchange environments , you must make sure that LAN, DB server, Exchange server are able to handle the load.
Also Outlook/Exchange has problems with 3500+ items per folder, so the user should make sure they archive old items or try synchronize to different folders.
This is the most common problem (GeniusConnect will raise errors and the sync will fail) and is related to most versions of Outlook/Exchange: http://support.microsoft.com/kb/905803
Outlook users experience poor performance when they work with a folder that contains many items on a server that is running Exchange Server
Microsoft Office Outlook 2003 users and Microsoft Office Outlook 2007 users experience poor performance when they work with a folder that contains many items on a server that is running Microsoft Exchange Server 2007, Microsoft Exchange Server 2003, or Microsoft Exchange 2000 Server. Additionally, Outlook users may receive one of the following messages:
Requesting data from Microsoft Exchange Server Outlook is retrieving data from the Microsoft Exchange Server ExchangeServerName
This issue occurs when an Outlook user works with items in a folder that contains many items. Outlook must perform several operations against the Exchange server to retrieve the contents of a folder. Therefore, when there are many items in a folder, additional processing is required to respond to the Outlook requests.
You can help avoid poor performance in Outlook by carefully managing the number of items in folders, especially the Outlook folders that are heavily used. These folders include the Inbox, Calendar, Tasks, and Sent Items folders and any other heavily used folders.
The recommended number of items in a folder depends on several factors. These factors include the client's proximity to the server, the storage infrastructure, the load on the hard disks, the number of users, and the number of restricted views.
We recommend that you maintain a range of 3,500 to 5,000 items in a folder depending on the capacity of the Exchange Server environment. Additionally, you can create more top-level folders or create sub-folders underneath the Inbox and Sent Items folders. When you do this, the costs that are associated with index creation will be greatly reduced if the number of items in any one folder does not exceed 5,000.
The following list includes ways that you can help manage the number of items in folders:• Use folder hierarchies to help keep the number of items in a folder to the recommended values.
• Use mailbox manager policies.
• Use client-based archiving solutions.
• Use server-based archiving solutions.
• Use mailbox size limits.