After reading very positive reviews for the Perovi Guesthouse on BedandBreakfastWorld and other booking sights, we received an email three days before our arrival informing us that the guesthouse was "moving" to new premises across town and changing its name to Old Tbilisi Hostel. The new location was in a very rundown neighborhood, found only by following a breadcrumb trail of graffiti signs. It turned out that the "guesthouse" had not moved at all but, it presumably being overbooked, its proprietors had shunted us to a room in a hostel. Our "private" room was separated from the lobby by a screen (not walls) and connected to another bedroom by an open window-type hole in the wall. For couples travelling together, even in private rooms, they include a large "No sex!" in the list of rules pinned to the wall. The Old Tbilisi Hostel itself is fine for a solo traveller but was very far from what we had booked and expected.
What really ruined our experience was the staff. The hostel was run by a couple of mumbling 20-somethings, and attempts to contact a "grown-up" manager from either property led nowhere. When we voiced our dissatisfaction at the last-minute change and decided to leave after one night, they showed no sympathy and charged us 50% of the entire remaining reservation just to escape.
Given that our trip to Tbilisi and interaction with Georgians were otherwise absolutely lovely, we just wanted to advise other travellers of the bait-and-switch these two properties are running so that your trip does not start off on a sour note.