We're all sweating little green beans for OS 4.3, and today RIM sends a press release talking about 2008 plans, including integration with Documents to Go (FINALLY) that requires an upgrade to OS 4.5:

Research In Motion

"1) Requires BlackBerry Enterprise Server v4.1.5 and BlackBerry device software v4.5 or above.
2) Microsoft Office Word and PowerPoint files will be supported in conjunction with BlackBerry device software v4.5 and Microsoft Excel files will be supported in conjunction with a subsequent software release expected later in the year."