I really like Twitter and all but with the recent issues its been having I was prompted by a friend's tweet to check out an alternate service, Jaiku.
Jaiku is definitely more evolved for a few reasons. First, it's possible to add more of your web presence to your microblog page. For example, feed Jaiku the URL for your Flickr photos or your blog and it will sniff out the RSS feeds for it and add each new post on any of those sites as a Jaiku entry. It's also more evolved in that there is the ability to comment on others entries which is a step up from prefacing responses on Twitter with "@{Name}." Also, you can add icons to each entry as a an added annotation. Playing a video game? Add the GameBoy icon to your tweet.
If Twitter gets their act together to make their service less spotty and they add some features similar to Jaiku then they'll secure their dominance in the microblogging arena. If not, then I see people migrating to Jaiku simply because it offers more.
In any case I'm on both for now. My Jaiku is here. For those of you that are Mac users you can download a Jaiku app similar to Twitterific, Juhu, here.