According to exit polls, John McCain won in several different demographic groups in the Florida primary, including seniors, moderates and Hispanics. Of these, the Hispanic category had the biggest disparity by far.
McCain won the Cuban vote 50-10 over Romney. And the non-Cuban Hispanic vote by 51-21. Those are gigantic differences, and can easily swing a close election like Florida. Since only 10% of the Republican voters were Latino, I'm not sure that Latinos were the decisive factor on Tuesday (but only because I have no idea how to do the math on that). But it's obvious that McCain's surge with Hispanic voters helped him substantially in winning Florida.
On the Democratic side, Hillary Clinton cruised to a meaningless victory (the Florida delegates don't count this year) also on the strength of large Hispanic support. This was also true in the Nevada caucus (which did count). She won the Latino vote by a 3 to 1 margin there -- and then won a narrow victory over Obama overall.
Latino voters are playing a crucial role in the primaries, and in some states, might play the decisive role. This is mainly because the vote so far has been so lopsided for one candidate as opposed to the other.
John McCain is winning out over his GOP counterparts because he is the only one who supported a halfway reasonable immigration proposal in the Senate, whereas the rest of the Republican field sounds like they want to drive illegal immigrants out of the country with a pitch fork.
Hillary Clinton's popularity among Latino voters has been a little harder to explain (the leading explanations are name recognition and the good record Bill Clinton had with Latino voters).
One thing is clear, once we get to the general election, if Latino voters keep voting with this big a gap between candidates, the Republicans are done for. McCain might sound halfway sane when compared to the rest of the Republicans, but his anti-immigration quotes can easily be used by the Democrats to turn Hispanic voters away from him. Let alone what the Democrats could do to any other Republican nominee on this issue.
Republicans have done a lot to damage themselves with the Latino community over the last couple of years. Those chickens are going to come home to roost in November, 2008. They wanted to chase a lot of recent immigrants out of this country, but ironically, some of those immigrants might be the one chasing them out of this race.