In many countries, shoes are seen as means for spreading infectious agents and some people like to keep their carpets clean by asking their vistors to take their shoes of. Do not be offended, it does not mean your shoes are ugly, it is a custom… So, if you see a pile of shoes at the doorway, take off yours, it is polite and you might even be offered slippers by the host. In Czech Republic, it is common to bring your own slippers. It is also a common practice in Finland (thanks to Jaui's feedback).