What a confusing thread...
Keep in mind, Outlook 2007 is only a client when it comes to mail. It is not a server, it does not host mail. Services like gmail, mobile.me, yahoo, hotmail all serve mail to the clients, whether they are web-based or device-based.
In order for mail to be sync'd between multiple clients (PC, iPad, iPhone) you want to use a service that either offers IMAP or Exchange. I realize that gmail will allow you to use POP3 and keep a copy of the email on the server after a client downloads the email, but from what I have tried, once one client downloads the email, it does not get downloaded again.
The average person who wants to keep mail sync'd between multiple clients will want to use IMAP. The server still stores all the mail and will update the clients when changes occur.
For me, I use Exchange, with Outlook 2007 as my PC client (on 2 different PCs) as well as my iPad and iPod Touch. All my mail, contacts and calendars are sync'd up pretty much instantly with iTunes not even a part of it. The thing with most Exchange services is that they are not free. I pay $2.99/month for mine from
Domain Names & Web Hosting : 1&1 Internet Inc. but it was a special promotion a number of years back from when they were beta testing their new services.
As for free versions of mail/contact/calendar sync, I would recommend IMAP from gmail over the other services out there. It is well worth the extra time to read through the FAQ's from gmail on getting your account set up right. You can sync gmail using the Exchange setting on the iPad, however I noticed some weird issues, including not all mail being downloaded to the iPad. It is best to use an IMAP account for email and the Exchange account for Calendar/Contacts only from gmail.