Quite simply, Obama has finally reached a point where he is polling ahead in all of the midwest swing states simultaneously, most likely due to his post-primary bounce and improvement among Democratic voters.  Obama now polls ahead in Michigan, Wisconsin, Ohio, and Pennsylvania at the same time, whereas for most of the primary season he was only polling ahead in one or two of those states at at a time.  These four states have a combined 68 electoral votes and have all been within a few percent in the past two presidential elections.

Obama has also improved his standing in emerging swing states where he seemed to show an advantage early on, such as Colorado and Virginia, where he now polls ahead in both.  9 and 13 electoral votes respectively, we haven't won either since LBJ in 1964 (except for Colorado in 1992 due to a very high Perot vote), yet have seen themselves become more competitive in recent years due to the changing demographics of those states.

Obama is also finally winning Missouri, a classic swing state that had slipped away from us recently. He defied predictions to narrowly win the state's primary, but went on to poll poorly against McCain. That has changed, and is worth another 11 votes to Obama.

Obama has also locked down Iowa and New Mexico pretty solidly, two Gore states that Kerry lost narrowly.  The former has always been a solid state for Obama since he won the caucus there and McCain skipped it, while the latter is moving towards being solidly Democratic at the local level.  7 and 5 votes respectively.

New Hampshire, a state that Kerry won that Gore actually lost, has also moved back to Obama, as McCain showed unique strength in that state this is not to be ignored.  Only 4 votes, but McCain finds himself not any stronger in the blue states that gave him his early primary wins and sealed the nomination for him.

And finally, Obama has nailed down all the solid Democratic states that people initially doubted his strength in, such as California, New York, New Jersey, and Massachusetts, while putting former swing states Washington and Oregon out of contention for McCain.

Where does that leave Obama?  Clearly with a big advantage going into November, McCain can only hope to narrowly win by running the table on every swing state, whereas Obama has the ability to pull states initially thought to be firmly in McCain's camp and rack up a huge landslide.  Yes, Ohio will be critical again, but we are in a different position this year.  We can win without Ohio.  McCain can't.  And with our growing strength in that state it's looking to be a long 8 years for Republicans under President Obama.

Note: Obama is also polling ahead in Indiana, a result I have difficulty believing, but he does seem to be stronger in this neighbor to Illinois than Gore or Kerry.