We have been using this product for over 7 years now, it has served us well with all of our communication needs in regards to customers, prospects, vendors etc.
I don't think there are any downsides at this time, but we would like more integration options between other products (ie Outlook). If you're looking for one piece of software that can help manage your entire sales process, look no further. It helps keep track of everything related to prospecting, as well as customer communications and documents.