According to the news reports DeepDyve's index consists of about 500 million pages already:
readwriteweb.com/archives/deep ...

deepdyve.com/

[Link updated to include www – Tony]

So deep, that deepdyve.com sends back an address not found :-)

Lots of hype and not much substance.

Wow, they have four subscription journals indexed! They proudly boast that their expert sources include "all of Wikipedia", which suggests that Google needn't be trembling.

deepdyve.com/why_deepdyve/expe ...

It is in Beta phase and there is DeepDyve Pro available too. That costs $54 in a month.
Source:
deepdyve.com/why_deepdyve/deep ...

Bad name, I think. People will naturally look for deepdive.com rather than deepdyve.com if you'd ask them verbally to check this site. Of course, it would be different if you'd take the time to spell it out or write it down for them. Find.com (find.com), another search engine, is smart enough to name themselves as such.