The are really only two cases where you can justify the laptop attachment for the Atrix:
1. You have the cash to blow and you just want a toy to have something new. Nothing wrong with that but for most of us $500 is not chump change.
2. You are a serious road warrior that travels a lot and carrying a minimum weight with you is important.
Otherwise, you are wasting your money. You can get a real net book or even a laptop for that kind of dough and it will outperform your Atrix laptop dock. And now that it has been rooted, it can tether with no problem.
And in 2 years when the Atrix is a fond memory of what was cutting edge in 2011, a netbook will still work as a standalone thing.
If the laptop dock were $300, it might be a justifiable toy. But at $500 it is serious early adopter tax.
My opinion, your mileage may vary.
David