Can an iPod Touch operate as a personal assistant?

The only things you can't do on an iPod Touch are use the phone-specific features of the iPhone:

• SMS messages via the native SMS application
  
• making and taking phone calls using the built-in phone application.
  
• Edge or 3G connectivity to the internet.

There are a host of 3rd party applications to send sms messages through their service (including google's web-based Google Voice client).

There are a few VOIP applications, like Skype or IAXDialer, which will work with other services than the ones provided by an iPhone's service provider (AT&T or the myriad of international mobile phone service providers).

PDA is the primary function for my iPod touch. I use it a lot more than I ever used my palm tx. I sync my google contacts and calender directly and use toodledo, evernote and paperless for to-do lists, notes and checklists.