A little detail and feedback...
I am always amazed how these types questions draw no or few responses and there are enough Dominicans (since it's a question about the DR vernacular) who post in the Spanish forum. However, when a response is posted some people contest or challenge it. Let's see what happens this time.
xamaicano, in my experience this is one linguistic feature in Spanish in general that's an across the board trait, not necessarily associated with a country, region, a group of speakers nor is education a factor or reason for the pronunciation variation. I do believe most Spanish speakers are 'ye?sta' means the /ll/ and /y/ are pronounced with a /y/ according to the phonetics of the language. However, you will hear the /j/ sound especially in words with /ll/ (in my experience) and more so if it's at the beginning of the word as quite a prevalent pronunciation or phonetic variance. I have a mix of both /y/ and 'j' depending on the word and I am not really sure why, when or how the inconsistency started in my own speech. Every now and then I would try to standardize but it sounds strange although phonetically the pronunciation should be with a /y/. The first twelve posts about /ll/ is discussed in this thread (
http://www.dr1.com/forums/spanish-101/65351-l-l.html).
I think more observation and research would have be done my part to say comfortably that it's heard more so in one region than another but in the DR you will hear the variance meaning the 'j' sound and also in the Caribbean without a doubt. As you said in your post it could be that you just had not noticed it, not paid attention to it or had not spoken to anyone who had the /j/ pronunciation emphasis up until now. As well some phonetic features are more subtle than others. Compare the /j/ sound to the cibae?o /i/. For example, on Sunday I try to make a few calls, family day per se and after talking on the phone recently I was thinking to myself how certain features of speech stand out if you don't hear them everyday-
'mi hija no te preocupe Dios te va a recompensai'. Long live
el cibae?o!
Also to note in some countries, the /ll/ in the middle of word is weak and sounds more like a /i/ when there's another /i/ and this may be a variation that you have not heard as yet either. For example,
gallina sounds more like
ga?na. This is more a trait of Central America.
In general, language is not a static concept. It's quite transferable meaning features of speech do get passed on from speaker to speaker, in some cases region to region and country to country. Some features of speech are associated with class level, or education, regional differences or a dialect but to my knowledge this is not one of them since it varies across the Spanish-speaking world (I am referring to Latin America). Some people (non linguists or language gurus) use the word dialect very freely when referring to regional speech varieties when in fact Spanish only has a few official dialects and
el cibae?o is one of them. Spanish is not like Italian a country with several dialects from region to region and from what I can tell they take precedence over standard Italian which is taught in school.
I think the /y/ and /ll/ change for /j/ by some speakers falls under the same linguistic phonetic study as
el seseo heard in Spain for starters and then further analyzed. The fundamental difference right from the get go is that
el seso is associated with a region because its not a phonetic feature of all Spaniards whereas the /y/, /ll/ phonetic variation is not regional as it is heard throughout Latin America.
-Marianopolita.