People often ask me if studying Ukrainian is confusing considering I study Russian as well (but no one ever asks this question regarding Norwegian and Swedish, and I don't really know why). Actually, it is a bit confusing. Many seem to think that since Ukrainian is so similar to Russian, it should be extremely easy to learn. I'm not sure those people have ever tried learning a closely related language, but if they haven't, they should give it a try. Some parts of it are obviously easier, such as shared vocabulary and grammatical structures, but the spelling can really get to you. It's the same thing for both Russian/Ukrainian and Swedish/Norwegian: almost every word that is of common origin is spelled somewhat differently. You will always understand the word, and for Ukrainian you can almost all of the time also understand what case it is in (even though there are confusing cases, like prepositional -ому, genitive -у and probably some other things that I have forgotten), so you don't actually have to learn these forms to be able to understand them both written and in speech. But in order to use them yourself... you know what word to use, you just don't know where the damned ь і ї will go this time!
Pronunciation is also a source of confusion, since Ukrainian е is pronounced like Russian э, and Ukrainian є is pronounced like Russian е, and Ukrainian и like Russian ы, etc. All of a sudden I find myself reading "развытые" instead of "развитие" out loud... And keeping track of all those non-palatalized consonant+е combinations in Ukrainian can be really tricky!
Today, however, I think I experienced problems writing in Russian for the first time. I caught myself adding third person singular/plural -ть endings instead of -т (формы изменяються, употребляються) all over the place, and of course while using a pen you can't erase. What is having the greatest impact on my Russian writing is the Greek alphabet though. I find myself unable to write small Russian Д and Ф. I have to start Р from the bottom all the time (compulsively) since that is how I do it in Greek, and that makes me confused and makes me go "wait... how did I use to write Р?" (answer: I have no idea!!). Especially trying to copy out a text in Russian explaining Ukrainian grammar with a Greek ghost hanging over me has had catastrophic results.
I've had a frustrating day (year, life?).
On the whole, I would say that I'm quite discouraged by how slowly I am learning Ukrainian. I know I should take into consideration that I have very little time for it. I usually don't manage to prepare anything for my language tandem meetings, so we only end up chatting, something I'm not convinced is very efficient for learning. I will continue struggling though, today with the use of the site http://tyzhden.ua/History/ and http://www.lnu.edu.ua/lknp/mova/in/ser/main1.html.
This is an interesting video in Russian/Ukrainian on Ukrainians living in Norway (thanks to Vera who showed it to me!):