Like Georgia, Ukraine became an independent nation when the Soviet Union collapsed. Like Georgia, Ukraine has in the last few years pursued a free market economy and ties with the west, leading to an economic boom. And when looking at Russia's current military actions in Georgia - which have expanded to include ground attacks in Abkhazia as well as South Ossetia, along with bombing of the airport of Tbilisi, Georgia's capitol - Ukraine can only be worried that it might soon be like Georgia in that respect as well.
Rather than hoping quietly that its turn might be deferred as long as possible, though, Ukraine is applying pressure. While Russia's Black Sea fleet is off blockading Georgia, Ukraine has warned the they might not be allowed to return to port. They can make this threat because that fleet is based in Sevastopol in the Crimea, which was ceded to Ukraine by Nikita Khrushchev in 1954.
It's a gutsy threat, though. While Ukraine's military is substantially stronger than Georgia's, it's not big enough to stand up to Russia. Perhaps more importantly, ethnic Ukrainians, while a majority in the rest of Ukraine, are only the third largest language group in Crimea, behind Russians and Tatars. Russia also has substantial ground forces in Crimea.
Should the U.S. do anything about this? While Ukraine is friendly with us, there's nothing that says we have responsibility for them. On the other hand, they were the first nation to voluntarily give up their nuclear weapons - they inherited about a third of the Soviet Union's weapons - largely at our behest, and we should be probably be grateful for that. On the gripping hand, Russia has a somewhat legitimate historical claim to Sevastopol. On the other gripping hand, probably the closest historical parallel to Russia's situation vis a vis Abkhazia and Sevastopol now is Germany's situation vis a vis the Sudeten and Danzig in the 1930s, and we all know how that turned out.
Of course, there's something we can do that doesn't involve combat. That is to send our Sixth fleet into the Black Sea. We wouldn't have to say a thing. Russia's Black Sea fleet would then be faced with a tough choice between continuing to blockade Georgia or making sure they could get back to port before we could get there. Giving them a tough choice would probably be worthwhile; in the long run, it would probably be better for Russia as well as for the rest of the world if they had to be a bit more careful before indulging in military adventures.
Article on Ukraine's warning to Russia: http://news.xinhuanet.com/english/2008-08/11/content_9155660.htm
Article on Dioxin poisoning of Ukraine's President, likely by the Russian government: http://www.timesonline.co.uk/tol/news/world/europe/article2426190.ece
The U.S. seems to be doing one better: sending in humanitarian relief using the Navy and the Air Force.
This is actually pretty clever. Russia claimed that they were not interested in invading Georgia, and were not going to cut lines of communication. The U.S. government is just taking them at their word, overlooking little indiscretions like Russia marching into Georgia's main port and sinking Georgia's navy. Now Russia is in a tough spot: either they have to allow the U.S. forces in peacefully, backing off their actions to match their words, or they start a war with the U.S. by shooting. Hopefully even Putin isn't stupid enough to start shooting us - or at least Medvedev is smart enough to stop him if he tries it.