Lots of people do - it all depends on the situation. Your ap has been in process at Buffalo since August - your medical results don't expire until the end of July 2011. Buffalo is currently finalizing spousal aps within 11 months, so you could get to a point where you might need/want to extend the validity of the meds to extend your COPR expiry - to give you time to land. If you got your initial assessment letter and they did not request any additional information, you can probably expect to be finalized before 11 months - and if they determine that there's enough time between the receipt of your passport to receive your COPR and the expiration date of your meds to facilitate your landing, they will probably not ask for a new medical.
From personal experience - our application started (re)processing in late April and my medical expiration was May 2011. They requested our passports at the very end of November, received them on Dec 15, and issued the COPR on Dec 31 with an expiration date of mid-May. So I had lots of time to land. That would be comparable to your passport being requested anytime up to about the end of March . . . and there'd still be plenty of time for a "leisurely" landing. And that would be 7 months in process . . . certainly within the realm of possibility for a straight-forward application. You could probably even push it to a passport request at the end of May - getting you your COPR by the end of June - and not have to worry. But you never know.
If it were me, I'd book a new medical now for the first week of June - just in case. You can always cancel it. Then, if you don't have a passport request by the end of May, you'd be able to quickly get another medical done, fax confirmation to Buffalo with your file number, and know you wouldn't be getting a request from them to redo one before they'd issue the COPR.
