I say this for a multitude of reasons. First, these are both difficult jobs, meaning that Martinez, already a so-so senator, will wind up doing neither of them ably. He'll piss off the voters for the next four years by hopping all around the country fundraising, and when the GOP gets stomped in 2008, he'll piss off the party machine, leading to less support in 2010.

Additionally, since the dawn of the 20th Century, four Republican senators have simultaneously served as chairmen of the GOP:
Marcus Hanna, the original Rove/Atwater type whose trail of slime put McKinley in office -- albeit briefly

Chairman of the GOP: 1896-1904
U.S. Senator: 1897-1904

Simeon Fess, swept out of power along with most other Republicans in the Depression years.

Chairman of the GOP: 1930-1932
U.S. Senator: 1922-1934

Thruston Morton, of the powerful Morton family, who ran the GOP in the 60s

Chairman of the GOP: 1959-1962
U.S. Senator: 1957-1968

Seeing a pattern here? Historically, every single sitting senator who has taken on the role of Republican chairman has lost in the next election. There's only one guy who bucks the trend, Viagra spokesman Bob Dole:

Chairman of the GOP: 1971-1973
U.S. Senator: 1969-1996

Well, Mel. I know Bob Dole. I proudly voted against Bob Dole in the very first presidential election in which I was legally able to vote. And you, sir, are no Bob Dole.

Chairman of the GOP: 2007-?
U.S. Senator: 2004-2010

Of course, it falls to the Democrats to find a viable candidate to oppose Martinez in '10, and the Florida Democratic Party is pretty short on viable, statewide candidates -- might as well start grooming Alex Sink now.

Alex Sink -- newly elected state CFO, and the only Democrat holding statewide office (other than Bill Nelson, of course)