What do you like best?
Sage X3 is great for multi-company, multi-site, multi-currency, multi-language, multi-legislation implementations. It is fully web-based, and system performance is generally quite good. It has very good intercompany transaction capabilities, and handles the "behind the scenes" multi-currency bookkeeping extremely well. While the built-in financial reporting is very limited, there are plenty of reporting tools out there - and since X3 stores the data in a very detailed manner, these reporting tools can display your data however you want. It is an incredibly flexible software which can be configured to perform very complex transactions with a high level of automation.
What do you dislike?
Error messages, when they do occur, are often quite cryptic and don't necessarily help guide you to resolution; also Sage's support for X3 is less than stellar. However, both of these issues Sage is aware of and working to remedy; it takes time with something as complex as X3, but progress is being made.
Recommendations to others considering the product
Have an experienced Sage Partner help you through the implementation. Take your time planning the implementation, plan it well - test it well - train well. It is extremely complex and a large undertaking. But if your requirements are fairly complex, then it is a really good product to answer your needs. But don't rush it!
What business problems are you solving with the product? What benefits have you realized?
Running multiple companies (some related, some not) - and currencies - from within the same accounting environment, allowing users to perform tasks seamlessly from one company/site/currency to another... Since implementing Sage X3, our accounting staff has realized a considerable improvement in efficiency in our complex accounting environment. And we are continuing to improve on this, as we gradually learn to take advantage of more and more that Sage X3 has to offer.