According to Lonely Planet's last edition, Summer Tavern "is still among the most popular hostels in Singapore". It is located 87 Victoria Street in the Colonial District. They even marked it on the map. The displayed phone number 6338 2381 doesn't work and if you ask a taxi driver to drive you there: you willl find out he has no idea of the street numbers. He will ask you which hotel you want to go and tell you that "no hotel this name". That's how I ended up walking from what the taxi driver considered as the "hotel district" to Victoria Street, 87, where there was no Summer Tavern to find.
I learnt from a quick search through the web that the address was wrong. Surprisingly, while they marked it on the Lonely Planet map, it is, in fact, in an other district.
Moereover it isn't a welcoming place. They usually don't bother to take calls or reply to emails. And it is quite expensive for what you've got.
If you want to stay there yet. The actual address is:
Summer Tavern
31 Carpenter Street
Singapore 059910