It doesn't take anywhere near remotely 7 days. Something is wrong with the way you've set it up. I have a similar setup with mail but it seems that Enom is down so I can't help you out with entry setup.
There seems to be one problem because Google says Note: Make sure each entry is entered exactly as it appears in the following table. Be sure to include the trailing dot at the end of each record. But yahoo automatically cuts that trailing DOTS.
its really a cool service; it took two days for Google to allow me and i just sent the values to my service provider to set every thing for me and they did it within six hours and it took about 12 hour for Google to read MX settings; thanks Mong for this thread!
Hmmm... I just wonder what would happen with your 1000+ accounts in future when Google decides to charge fees for the service (I heard rumours about that)... Some company or so would probably pay for the service, but would you pay for your users?