Consider your need for:
- shared calendaring
- shared meeting room/resources
- shared contacts
- Active Directory integration
If these features appeal to you, you may with to consider moving to an Exchange setup. You don't have to purchase/license Exchange and all the servers, however. There are a handful of good Exchange hosts out there that can really help your bottom line (if you pick the right one for your needs).
Shared/hosted Exchange means that you don't have to worry about:
- uptime, 24/7 power and internet connectivity
- spam filters
- server performance(RAID, memory problems)
I've taken onboard the task of integrating Exchange into the SMB, and it's something that needs a bit of research and a good resource. It can be expensive (depending on your budget), and if it's not in your core competency, or I.T. isn't in your company's core competency, it'll be a challenge to convince the CFO/Controller to dish out the cash. You may have to prove out the benefits, or have the users complain loudly enough.
Run the Numbers!
Perhaps run the hosted Exchange scenario through a spreadsheet. Costs of purchasing and running inhouse vs. hosted. Run it for 2, 5 and 10 years. Remember to include your company's expected headcount in those time periods.
Keeping the POP3 Status Quo
If the users aren't screaming for the features of 'Outlook' like they had in their last job, and you can manage the above issues, then perhaps the move to Exchange isn't for your organization yet. Nothing wrong with that!