I've been using SeeFusion for the past couple of weeks and I have to say, I'm not quite sure how I managed ColdFusion servers without it.
The first place it has been a huge help is in load testing. In the past my company has only monitored servers via Windows Perfmon. However, because we are running the multiserver enterprise edition of ColdFusion we don't have access to the ColdFuison Perfmon collectors. We have monitored things like disk usage and memory, which help give a sense of how the server is doing as a whole, but don't really give much insight as to what is happening with ColdFusion. With SeeFusion I'm now able to collect metrics such as slow pages and queries as well as other counters which will really help me identify bottlenecks and tune the application.
SeeFusion has also made troubleshooting a lot easier. We recently had an app which was running slow, but I wasn't sure where the problem was. Using SeeFusion I was quickly able to determine that the issue was with the database. I was even able to pinpoint one query that seemed to be the source of most of the problems... And I haven't even gotten into active monitoring rules yet, but I'm sure these will come in handy once the application goes live. (Active monitoring rules let you take action, such sending an email notification or terminating a request, when certain server conditions are met.)
I evaluated both SeeFusion and FusionReactor in my quest for a ColdFusion monitoring tool but ultimately decided on SeeFusion for a number of reasons. First, my host uses SeeFusion. I know other hosts use FusionReactor, but knowing that my host has had success with SeeFusion definitely influenced my decision. Also, I recently saw Daryl Banttari of Webapper, the makers of SeeFuison, give and excellent presentation at cfObjective. While he did use SeeFusion during his presentation, it certainly wasn't the focus of his talk. However, just seeing someone from Webapper out sharing their knowledge made me give greater consideration to their product. Finally, the enterprise version of SeeFusion was considerably less expensive than the enterprise edition of FusionReactor. While FusionReactor does seem to have a slightly slicker interface, I'm not sure there was a big enough difference in functionality to justify the price difference.
Of course ColdFusion 8 has server monitoring built in, but lets face it; if you are running a huge application on large cluster, you are probably not upgrading to CF 8 anytime soon. (I'm sure that quite of few applications are only now being upgraded to CF 7 due to the fact that CF 6.1 is no longer for sale.) In the meantime, SeeFusion is a great option for ColdFusion server monitoring.