The inability of SSMS to handle large (e.g., 50MB+) script files has been significantly reduced its utility and been a hindrance to productivity. In working with large database update scripts, I was trying to take advantage of regex search and replace for enhancing the scripts. But, on a PC with 1GB RAM, I was unable to save the changes, encountering the error message "The operation could not be completed. Not enough storage is available to complete this operation.". And I was frequently unable to copy and paste usefully large portions of the changes, getting the error "The selection is too large to copy to the clipboard. Please make a smaller selection and try again."
In both scenarios, SS2000 Query Analyzer consistently handled these operations without issue -- even when SSMS (SqlWb.exe) was still running and consuming significant memory.