Conflicting sources on this.
confidently says the 945GMS chipset is as good as it's going to get for a while - Poulsbo chipset being for the lower-power Silverthorne Atom only.
But Anandtech's Dell Mini review
I asked Dell why it opted against Poulsbo and I was told that it was a timing issue - in order to have the Inspiron Mini out today, the design had to be completed using 945G. I'd expect future netbooks to start switching to Poulsbo, but for now we're strictly a 945G shop.
My impression is that Poulsbo would work, and be better for performance as well as efficiency (it's cited as supporting 1080 px video), but is a lot more expensive. Maybe the success of netbooks among affluent populations will lead to segmentation of the market, and a higher-priced Poulsbo class - I think a lot of us would be happy to pay for the gains it would bring. (Intel seems to have a party line based on a somewhat condescending preconception of what the market for netbooks is, and it leads them to say things which confuse people.)