Currently the estimated time for citizenship is way longer than it used to be and probably will get better in the future by the time you are eligible. 2007 had a huge increase in the fees to apply for things, therefore whoever could file by the deadline last july did it resulting in a gigantic amount of applications that clogged everything up. I think I also heard somewhere that since citizenship applications are the least urgent to process, they kinda were put at the bottom of the list to give priority to other types of things. It might and probably will get better as I said, but yes, be prepared in case it doesn't, even before 2007 there were always a few cases that took longer than "normal".BTW it appears that some district offices are already past the july backlog, as a matter of fact there are a few people on VJ who filed for citizenship in november and december 2007 who currently have an interview date, so it seems things are getting better already, at least in some places...(not Baltimore as you can see from my timeline in my signature).
Good luck when the time comes!