I wouldn't say I hesitate to talk about life on Mars, especially after yesterday's announcement. It's just that all we know is the high probability early Mars was wet (caveat: I'm waiting for Nick to rehabilitate his models and challenge wet Mars again). While I think that life's inevitable when conditions are right (my slogan: "physics begets chemistry begets biology"™), nobody's actually found signs of ancient or extant life. Nevertheless, it does feel like I have more "permission" now to speculate.

The chemistry you focused on is the most crucial factor, of course. The other thing I like to consider is how the topography of Mars would shape an ancient wet environment. Reasonable computer simulations of water on Mars don't show oceans or even seas, but more a vast network of interconnected crater lakes. So the ancient environment would've been significantly different from ancient Earth: A far higher ratio of coastline to water (a highly fractal coastal environment with lots of tidepools and sheltered coves); and a complex history, as water levels rise and fall and lakes are connected for a while, then isolated for a while, then connected again. On Earth species have been occasionally divided as land bridges appear and disappear, leading to divergance of species; but on Mars it would've been routine. I'd expect much more speciation, punctuated by periods of intense competition as isolated lakes are reconnected when water levels rise.

The result, I think, would've been life even more adaptable than on Earth. It would've been brought routinely to the brink of extinction by frequent dramatic local changes in the environment; and life (through evolution) would've responded by "learning" mechanisms to survive rapid catastrophic change, like dormancy and spores. It's logical to suppose that if life ever did get started on Mars, there's a nontrivial chance it's survived to the present in some nook or cranny of the planet. "That which didn't kill it made it strong."

Or I could be completely wrong. There's a long ways to go before we know the answer to the question of life on Mars...unless tomorrow one of the rovers images a microfossil. We sure do live in interesting times, don't we?