Outside of the Google Hype, there are three major disadvantages with using Google Apps:

• Handling of multiple email accounts is very clumsy. GMail lumps all the emails into one inbox. You can set up a "Label" for an email address - buts its nothing like having separate inbox/sent/trash like Windows Live, Outlook and Thunderbird.
• No mail folders - just mail "labels". The main disadvantage here is that Labels are only single level - there are no sub folders. Google's method is to rely on searching and not filing.
• No desktop App. Its all webbased and relies on your browser and Internet connection. The data is all kept online. There is an offline facility for google apps gmail - but we didn't get as far as using it. I'm not sure what happens when your Internet Service is down (or slowed to a halt) - I'm guessing it would leave you dead in the water.

In short - if you are the type of person that doesn't sort your email, has 100000 of emails left in your mail box, and only one mail box, then Google Apps maybe for you. Alternatively if you only keep some emails and bin the rest - the Google apps will be fine.

There are lots of pro's for Google Apps - but you can visit the Google marketing machine for that info.