Can you say more about why the use of strategic bombers and seeming preparation for a thrust at the ports suggest that the Russians are going for Tbilisi? Couldn’t the first two just be to “up the pain” on Georgia, in the hopes they’ll “give up” on whatever (perhaps, to date successful) resistance they’ve managed to mount against the 58th Army in South Ossetia?

That’s a manner of speaking. The Russians don’t have to take Tbilisi to cut up Georgia. But they had better, otherwise it would have been like attacking Iraq and stopping short of Baghdad. In other words, an unstable position. The Russians have already gone too far for their own good. Had they pulled back they could have made their point and acted the savior of the Ossetians. In a little while it will no longer be “about” Ossetia. It will be about Russia. There’s still time, but it’s ticking away.