It's exactly like you don't sound the 'h' when saying 'hour'. This may help a bit more: http://www.italki.com/answers/question/66555.htm

In grammer or writing, we have to use "좋아요". But when people speak out it, we eliminate "ㅎ" Like "Handsome" We don't pronounce "d". It's same way. :D

"조아요" is correct. We usually don't sound 'ㅎ' when the 'ㅎ' is located below (I mean "받침") and the 'o' follows it. e.g. 않아요 - 아나요 괜찮아요 - 괜차나요 많아요 - 마나요 But when you say "좋다", it sounds like "조타" e.g. 많다 - 만타 괜찮다 - 괜찬타

There are many Korean word that it is not same letter you can listen. It dose not maken by it was sounded. For example, '전화' it sound like '저놔', '행복해요' it sound like '행보캐요'. and There are many case in Korean word that it does not make a sound looks like 'honest' in 'h'. For example, '좋아요' it sound like '조아요'in there is no 'ㅎ' sound. But many times in internet there are many Korean young people say '조아요' when thay want to express '좋아요'. Thay think it seems more cute and precocious but its not correct in grammar.