The destruction of Soviet Union about 15 years ago, made a huge country with a great level of IT science divided into small bricks. Nowadays, despite Russia's expansion into world software development market, Ukraine keeps playing an important role here too. There are several prerequisites for this.
Traditionally, Ukraine always was a technical region of USSR. No wonder, IT education was and still is one of most popular and respective education in region. Such well-known Ukrainian universities as Kyiv National Technical University, Donetsk National Technical University etc. as well as new establishments with more innovative approach for IT specialists education, such as Donetsk State Institute of Artificial Intelligence and others, educate a new prospective generation of young IT professionals, ambitious and purposeful.
It's obvious, Ukrainian students win in international contests, and show true professionalism and ability to enter a business life immediately, hence, to play first fiddle in labour market. As latest example, one can remember students of Kharkiv National University of Radio Electronics that became first place winners of International Web Development Contest (I.C.W.D.I.C. 2005) held by XITEX Software Company in spring 2005.
That is why governments of European countries encourage Ukrainian programmers to come and to work there. Germany is best example of a country that understands all pros and cons of Ukrainian IT professional, thus it's country that sees its benefits of employing Ukrainian programmers.
Another one important factor is cost of labour. In Ukraine, usual hourly rates for programmers are $10-$15. Although they are little bigger than Indian ones, they are still 1.5 times lesser than Russian ones and several times lesser than American or European costs. If you consider high level of professionalism and responsibility, then you add a European mind and time zone, plus a fluent English of most of IT people, you realize that Ukraine is that happy medium each company looks for. Hence, many companies that outsource have already realized it.