Eventually I visited it a few months back; my girlfriend had been recently and said it was OK.
Unfortunately it seems that you really do have to get lucky to find a member of staff there who knows what veganism means; whilst she'd gotten lucky, on our trip I'm not convinced we found one.
You'd be forgiven for thinking that with a name like Cafe Soya that it must be a veg restaurant. It's not, in the slightest. They do have a separate vegetarian menu, but nothing is marked and no one who was working there the evening we went seemed to have a clue what was vegan and what wasn't.
When we'd eventually communicated as best we could, they took our order. Spring rolls and mock duck for starter, sweet and sour tofu, steamed rice and another tofu dish for main:
If I'd have eaten there 10 years ago I expect that I'd have been pretty impressed. Since then however I've been both spoilt by places like Veggie World, and learnt how to cook my favourite dishes at home. As such, considering the food was rather mediocre; I wasn't overly taken by my trip to Cafe Soya and shalln't be rushing back.
I had a similar experience with a restaurant in NYC...It was called "Soy Cafe" or something of the like. The vegan offerings were few and disappointing.