Has anybody used this TI PDF 8575 chip?

http://focus.ti.com/lit/ds/symlink/pcf8575.pdf

I'm working on a very low power application where we need a few more IO pins
than what we can get on the microcontroller and the project lead is
recommending this. It's basically an I2C addressable shift register, but it
claims to allow any pin to be an output OR an input without having to set
any direction bits. (!!!)

I can't get my head around how it can have pins that are inputs, and others
that are outputs without any direction registers in it. As far as I can see,
it drives any pin that you write out a 1 to with 1mA to the Vcc rail. So
they are fairly easy to overcome with an input that may need to drive that
pin low. Sort of the standard open collector with a pull up deal. No problem
so far. 

But then they have something called IOHT that drives any pin that set high
hard to Vcc until after the last clock.

"An additional strong pull-up to VCC (IOHT) allows fast rising edges into
heavily loaded outputs. This device turns on when an output is written high
and is switched off by the negative edge of SCL"

So what are we saying? That its ok for some other device that is trying to
drive a low into one of these pins to drive against the supply rail as long
as you only do it for a little while?

His statement is that this will require less power over all than will any
standard available shift registers. Isn't even the 1mA pull up going to suck
down the juice for any input that happens to be a zero? Not to mention the
ton of juice whenever we write out new values to the output pins and that
zero gets driven high at full power for the time between the bit and the
last clock?

Am I missing something here?

I've been looking for a set of good low power shift registers (one in and
one out), and I have to admit, I can't find anything that will pull less
than about 100uA in normal operation (not including what ever it is driving
as an output). This PDF 8575 has an Icc of 75uA or less in operating mode
and will standby down to around 3uA.

Help?

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