I've had a chance to read the opinion (the link in the original post is apparently dead -- you can find the opinion here
instead). A few observations:
For those few people who might not have committed the text of the seventeenth amendment to memory, here is the relevant section:
The authors of the seventeenth amendment wrote:
When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
The court analogized the governor's duty to issue writs of election in the case of senatorial vacancies to the governor's duty to issue writs of election in the case of congressional vacancies, which is found in Art. I, sec. 2 of the constitution, and which simply states: "When vacancies happen in the Representation from any State, the Executive Authority thereof shall issue Writs of Election to fill such Vacancies." That clause has been interpreted as mandating elections to fill a congressional vacancies. The only difference is that the seventeenth amendment permits governors to make temporary appointments to fill senatorial vacancies. The question, then, is whether "temporary" means filling the seat until the next regularly scheduled congressional election (as has been the traditional interpretation) or filling the seat only until a special election can be held (which is what the petitioners in this case argued).
The court, analyzing the congressional debates over the seventeenth amendment, concluded that the drafters envisioned a situation closer to the way vacant congressional seats were filled, i.e. the governor would announce an election within a short period of time after the vacancy occurred. The governor could name a temporary replacement, but that replacement would only serve until the state could elect a replacement.
The court recognized that the governor's power to call an election could be limited by the legislature. In the case of Illinois, the court concluded that the legislature only allowed the governor to pick one day on which the election to fill the Obama vacancy could take place: Nov. 2, 2010, which just so happens to be the date on which the regular congressional election is scheduled to take place. The result, then, is that Illinois will have two senatorial elections on that date: one to fill the remainder of Obama's term (which expires on Jan. 3, 2011), and one for the regular, six-year term to begin on Jan. 3, 2011.
There is no indication yet that the state will ask the full circuit to review this decision or if it will appeal to the supreme court. The seventh circuit covers Illinois, Wisconsin, and Indiana, and this decision only applies to those states.