I was using my POI Utility ColdFusion custom tags to create true Excel reports for a client. Some of the reports that they are running were really long (thousands of rows) and the reports were just dying. I had to do something, so I went into the POI custom tags and totally reengineered the way they work. Rather than creating a new instance of the CSSRule.cfc ColdFusion component for every single cell.cfm, I am now creating only one instance of it and caching it in the document.cfm tag. Instead of it housing the CSS properties for a cell, I rebuilt it to be merely act as a utility object to which CSS "struct"s are passed. The drastic decrease in CreateObject() calls was enough to give a good performance boost. In addition to that, I have also cut out as many method calls as I possibly could. On large reports, even calling a simple method could add seconds to the processing time. I am now relying on StructAppend() to take care of must of the cascading logic of "cascading" style sheets; this has also proved to be a good performance boost.
Since I was in there, I have fixed the last few outstanding ColdFusion MX7 compatibility issues. I have also moved the above performance updates to the CFMX 7 version as well. I hope that doesn't create new CFMX 7 bugs (I ran it on a CF8 box and at least it didn't error out for syntax reasons).
The updated code is available from my POIUtility.cfc Project page.