I've worked for a ~100 person company that switched from Exchange to Zimbra last year. While many aspects of the system work great, others are buggy, difficult

I've worked for a ~100 person company that switched from Exchange to Zimbra last year. While many aspects of the system work great, others are buggy, difficult, or practically useless. (For example, the calendar features are miserably immature, and the web interface is clunky and eschewed by most employees.) The company is currently considering switching back to Exchange.