One of the most interesting charts produced by Ofcom recently (2010 data) is an analysis of the enthusiasm of online consumers - how often do you buy online? Poland is a very interesting edge case:
OK, spend per head is not so high, reflecting its relatively low GDP per head, the value of the Zloty, and its economic development stage. But just look at that spend frequency: second in Europe only behind the UK! (and the UK is a weird edge case anyway, nowhere else are consumers as enthusiastic about online retail). There is anecdotal evidence that other very developed E.European markets, especially Czech, show similar behaviour, but unfortunately no data.
And online customers are growing fast, as this data from the 2011 Ofcom report shows:
Already ahead of Italy and Spain (where customers seems to like to browse online but not purchase), catching up rapidly on Ireland, and showing similar growth to France.
So if you are looking to reach out to another customer market, have a serious think about translating your site into Polish... There are some other advantages to Poland too. Delivery infrastructure is well developed, with major players like DHL well established, and payment methods are less "eccentric" than some other apparently easier potential markets (e.g. Netherlands, France, Germany, Belgium or Denmark all with challenging local schemes).
There's just one snag... in some categories everyone else is there too, especially the leading retailers from Germany and France. If you fancy somewhere a bit easier but with similar characteristics, try Czech. There are only 10.2M Czechs compared to 38.5M Poles, but there's a lot less competition as a consequence. Tesco are, however, using it as their pilot country for eCommerce in E.Europe, so move fast before it's taken!