oh yes very gutsy , we did have other servers we could point to and run the reports if everything went to pot, so not AS scary as it sounds. One thing we found extremely problematic was converting all our applications which used ReportService.asmx to generate reports. As they need to use reportexecution2005.asmx (I can't remember if that is right now?)
We use a webservice to generate a lot of our reports into Excel, which was the biggest trouble maker.
Several Reports are stitched together in Excel but the way ReportingServices deals with rendering to Excel is slightly more interesting. when we stitch our reports together we copy the individual reports into one workbook. A lot of the formatting was then lost, colours especially, as the first sheet that is created is the Master, This Master sheet, references all the colours used, if you add more sheets to the Workbook that the master is in, only the colours used in the master are used, and excel will Badly Guess the other colours, sometimes It will give you something entirely random, ie instead of a pale green , it will use BRIGHT RED.
If you try copying an excel rendered report to another sheet you'll see this problem.
Also the other Annoyance which turned out to be not much of a problem, is that CanShrink and CanGrow Attributes are useless in excel. Excel doesn't translate it , and reports come out in a variety of different sizes. to solve this I was about to painstakingly set each CanShrink and CanGrow to false, and then i realised I could just do a find and replace for all values and set them all to false in one go.
Possibly saved me about 2 days worth of hard tinkering.
I solved my RED CROSS Problem , I deleted the groups that were inside the objects and reapplied them. Problem solved , although , nothing told me why they were caused, or how it should be solved.