Re: Contact Lockin: Your contacts should be in the Directory Server and synced to Google Apps. Any first class platform you will migrate to will sync to LDAP.
Re: Calendar I've done two calendar technology migrations for 500+ person companies - they are typically forklift upgrades done over a weekend. You basically lock in your resources (rooms, typically) a week ahead of time, have people rebook any forward meetings into those resources - and have everyone switch into the new system on Monday. As long as people have the right client (in Googles case, that would be a "Web Browser") there is no lock-in.
I could take a 500 person company from Google Calendar, Email, and Contacts over to Microsoft exchange with a team of three people in under a month, with maybe 2 days of disarray (monday) as people (who ignore instructions the previous week) update the mail servers and LDAP servers on their various Androids, iPhones, Macintoshes, etc...
Just make sure you keep your primary directory in your own LDAP server, and you will be good to go. Don't outsource the directory. And stick to something LDAP compatible.
Yeah, it's reasonably light, as I said. Training and end-user usage patterns (never something to be taken lightly) are probably your biggest issues.
Then again, the user experience with the leading alternative solution (MS Exchange) is so miserable that at one organization I'm aware of, the public announcement of a migration to Google Apps for Domains was greeted with a standing ovation.
Re: Calendar I've done two calendar technology migrations for 500+ person companies - they are typically forklift upgrades done over a weekend. You basically lock in your resources (rooms, typically) a week ahead of time, have people rebook any forward meetings into those resources - and have everyone switch into the new system on Monday. As long as people have the right client (in Googles case, that would be a "Web Browser") there is no lock-in.
I could take a 500 person company from Google Calendar, Email, and Contacts over to Microsoft exchange with a team of three people in under a month, with maybe 2 days of disarray (monday) as people (who ignore instructions the previous week) update the mail servers and LDAP servers on their various Androids, iPhones, Macintoshes, etc...
Just make sure you keep your primary directory in your own LDAP server, and you will be good to go. Don't outsource the directory. And stick to something LDAP compatible.