Some towns only have one place worth staying at. The Koala Den in Potosí is one of those places. Quite friendly, with a nice little lounge area to chat with ye 'ol fellow travellers, and a great TV / dining room as well (excellent collection of DVDs!). Also has quite an extensive 2-for-1 book exchange collection. And, very importantly, it's a warm "den" (as its name suggests) in a very cold town.
Rooms: clean, with private bathrooms, and quite warm (they have heaters in the rooms).
People: every gringo passing through town stays here, so a great, social crowd.
Staff: accommodating, and even speak a tad bit of English.
Location: quiet little street, a few blocks from the centre of town.
Food / Internet: impressive free breakfast of bread, eggs, fruit, and tea / coffee. Free Internet coming soon (they were building the desks when I was there).
Hot water: ever-present, and very much ever-needed (especially after a filthy mine tour).