wow, noticed how everybody here types in proper capitalization and punctuation! definitely feeling the social pressure to conform
i think yeah, forums and online chatting and its relatives are good for gradually building up your social skills. it gives you the time you need to carefully write/type exactly what you want to say. but i think past a certain point, you just don't grow anymore, or rather you hit the point of diminishing returns. also, it does have its downsides; you start caring way too much how you might come across depending on what you say, and you have to rationally think about everything you say or do.
there was this study on communication that shows that only 7% of it is verbal, 93% is body language and voice tonality! forums and online chatting can help you in that 7% department, but in the end you'll have to work on the 93% anyway.
i do realize that if we're starting out, it can be hard, and any growth we can get is worthwhile. but just realize that you don't need to pretend to be somebody you really aren't. you don't have to say any "right" or "wrong" thing, you just speak as who you are. so it is much more a factor of who you are as a person. communication is just an expression of that.
on that note, i believe the easiest way to genuinely believe you have something to share, is to become the kind of person who does have something to share and knows it. lead an interesting life, develop hobbies that you are passionate about, learn new skills like humor and storytelling, etc. i believe steve pavlina has already done a good job on these topics
as you develop yourself, you realize that you really do have a lot to give to others, and that talking to people is FUN!
i started out being very shy as well, and antisocial...and at times, i still do...but once you make a conscious decision to improve (for me, i wanted to get the area of dating and relationships handled once and for all), you really start growing really really fast. anyway, just my thoughts, GOOD LUCK! i've recently read "tuesdays with morrie" and in it they say, relationships and connections with people are all that really lasts, really matters in life, and now im beginning to agree.