I love Twitter - I really like how you can use twitter on your phone or on the web - I use it to stay in touch with my friends, ask questions, gather information and even get some news. Early on I found that using the web interface (twitter.com) was a bit limited and after trying a few different desktop applications decided that Tweetdeck worked best for me. I could group people, I didn't have to constantly check for updates. Even though I use Tweetdeck I still end up using twitter.com quite a bit. Well there is a modification to Twitter.com that you can do through firefox that makes using the web interface a lot more fun.
Troy's Twitter Script is a firefox extension - follow the instructions (you download the greasemonkey extension and then Troy's script) and all of a sudden your twitter page looks like this:

Sorry about the quality of the screen capture I did this very quickly. All of a sudden conversations are nested- you can follow conversations and replies of friends even when you aren't following their friends. Videos and photos get expanded, you can watch them right on the twitter.com page.
This is a really nice modification - there is a group function but I haven't been able to see how you use groups yet. The script also adds a RT (retweet) button to make it easier to pass on tweets you have found useful. It also expands out the URLS so you can see what you are about to click on (instead of just the URL shortner like tinyurl.com)
There is also a way to add social links to twitter profiles (another feature I have yet to play with) but another great way to build connections with people.
This is an easy modification - but only works with firefox. Learn more about this Cool Twitter Script
Almost forgot, be sure to follow me on twitter @cgjerdetu