What issues are there in using Gmail for a corporate email solution?

Google has a corporate solution called Google Apps. Your company could consider using that. The paid version of Google Apps has service level guarantees, which could be better than what your internal IT could provide.

As for advantages, Google has better spam filtering than most other email providers, because they have so much mail data they process (through their public Gmail service).

Disclosure: I don't work for Google nor have any relation to them. I do have domains on Google Apps, and I have also worked for places that do.

I have switched our company to Google Apps Enterprise, so I thought I would give some feedback based on an actual switch. So far, the switchover has been pretty smooth, and practically all user's old email has been able to be uploaded to the Google servers. Although it is a valid concern that Google could do something that would lose our data, it is much more likely that they will do a much much better job than we on infrastructure maintenance. About 10% of my users have been grumpy about the switch. Here are the valid grumpy comments:

1) Google Web Client does not allow the forwarding of multiple emails.

2) Attaching multiple attachments via drag & drop not possible.

3) Having to attach files individually and wait for them to upload is annoying.

4) They are used to folders in Outlook/Mozilla and refuse to abandon folders for the search function.

5) Heavy folder users have a hard time understanding the difference between folders and labels, and the fact that labels are not hierarchical.

6) No drag-and-drop onto labels.

Since an email client can still be used with the accounts, I have helped a small number of users configure their fat clients to connect using IMAP. In the future, only the web client will be "officially" supported.