Call me ungrateful, but I'm unimpressed with Bush's Mars announcement. It's not really a plan - there's no funding, there's no technology initiative, no particular insight except "um, go to the moon first". It's baldly political. And with a first deliverable 16 years in the future, it's free of presidential responsibility.
In the meantime the US is already at Mars via robotic landers. With a less than 50% success rate to Mars it seems prudent to send robots instead of people. Better science too — concentrate on investigation rather than protecting fragile humans. Space telescopes like Hubble or WMAP seem much more valuable (and cheaper) than planting a flag and radioing the president from Mars.
I understand the romance of sending people to space. But aren't we past that? And it's not like we can do both: without significant new funding what this Mars program means is that we don't have resources for robotic missions, space telescopes, etc. For the next forty years NASA is all about flinging meat to Mars.
PS: this editorial calling for one-way manned trips to Mars is pretty interesting.