If you went back in time 25 years ago and said "in 25 years time the geeks will be cool" I think no-one would believe you. 25 years ago geeks like me were fiddling around with the BBC B and the cool kids had guitars.
A few highlights over the years:
I worked for a company that was on the internet before the web was invented and we had gopher and wais, but most of all Usenet. Then Mosaic came along.
A bit later I heard the internet mentioned on the Radio 4 News Quiz (still going). Then URLs appeared on adverts. The internet was becoming mainstream.
There were online journals and then Peter Merholz invented the word "blog". I was reading his blog at the time.
Blogs became mainstream and Gary Lineker said during the World Cup 2006 (I think) "what's a blog?". He probably knows now.
In 2006 Twitter was launched. It was called twttr at first because we were short of vowels in those days (see Flickr). I was the 791st person to sign up. Now there are millions of users.
A year or so after that I heard twitter mentioned by a radio DJ, but it didn't have a high profile and it was still in the realm of us geeks. Us geeks love to rush around saying "jaiku!" "friendfeed!" "diggit!" and other Latest New Things. However Twitter is now mentioned regularly on TV, radio and dead tree media so I think I can safely say
Twitter is big