According to an April 7, 2011 press release from the United States Patent and Trademark Office:
In the event of a government shutdown on April 9, 2011, the United States Patent and Trademark Office will remain open and continue to operate as usual for a period of six business days – through Monday, April 18, 2011 — because the USPTO has enough available reserves, not linked to the current fiscal year, to remain in operation until then. Should a shutdown occur and continue longer than the six-day period, we anticipate that limited staff will be able to continue to work to accept new electronic applications and maintain IT infrastructure, among other functions.
IP Spotlight 
Thank goodness the shutdown was averted … for now, at least. The patent office really does not need any more difficulties in funding its operations.