I could spend quite some time formulating my opinion on this question, but instead I recommend reading the debate on this issue at the Central Europe Active blog. Just a short statement:
If it wants, an internally united Ukraine should get a membership perspective for the European Union; nevertheless, the process will take quite some time and enormous efforts.
But before you go to the debate, please first stop by at Dante's Vitaliy's 8th Circle, because he was so kind presenting the translation of some recent figures on the public opinion in Ukraine concerning the accession of the country to the European Union. The figures confirm the divide of this big European country, although they leave some room for interpretation. Vitaliy does this in a more optimistic way while personally I would show some restraint.