How can I accept iCalendar / MS Exchange meeting invitations on the Nexus One?

Android (as of 2.1) doesn't handle iCal or Exchange meeting requests out of the box. In order to accept or deny meeting/appointment requests, you'll need to install an Android application called Touchdown via the Android Marketplace.

Unfortunately, Touchdown isn't free. It costs $19.99, so for now you'll have to cough up $20 for improved Exchange integration on Android.

There are a few rumors out there that Google is actively working on improving Android's Exchange support, but no confirmations.