I agree its probably about capacity. iPhone users already use more data than the average data plan subscriber, so they probably estimate iPhone tetherers will also use a lot more data.
AT&T has been consistent lately about pricing the iPhone plans just like any other phone plans--I don't see why they wouldn't offer a 5GB capped tether plan for an additional $30.

Another possibility is that they're having trouble distinguishing tethering from normal use--possibly if they enable tethering then it might work even when not paying for the tethering plan. That would be a deal breaker for them.

All of it smells to me like Apple is trying to make their issues with AT&T obvious. It's very possible that Apple has a CDMA iPhone in the pipeline for 2010, with or without LTE. Consider that it took 2 years for the new graphics chip to reach market after the supply deals were made and that last year Apple was headhunting CDMA2000/EV-DO engineers.

Last I checked, tethering is an extra $30 over your normal plan. If you're getting it for $10-12, then that's some legacy rate and not available for new customers.

Its not that they are hardcoded to block MMS, they are set to intercept MMS and use the viewmymessage.com portal for them. You can still get MMS using an iPhone right now, but it comes in the form of a SMS with a login and password.

I sincerely doubt AT&T will charge extra for MMS. They just have to figure out how to selectively pass MMS through to iPhones using 3.0 and continue using the portal for iPhones using 2.0.

I'm am still shocked at the lack of technical understanding being applied to the idea that AT&T will charge extra for MMS.

Those would be two good targets for LED lighting. Both are directional lighting and can be designed with non-standard fixtures. You'd probably never need to change the fridge LED, and bathrooms could have some stylish designs that aren't built around the shape of an ancient incandescent light bulb.

Ceiling fans could benefit from LEDs too. The vibration is bad for incandescents. Depending on your wiring, the fan motor may be rough on your CFLs.

Blended use of CFL and LED is the way to go.