I am looking for alternatives to Twitter. In particular, the annoyances I am looking to fix are:Twitter does conversations really poorly. The replies aren't grouped with the messages they are replies to.Twitter limits how many characters can be usedTwitter is not designed to help deal with noise (see the next two bullet points). Google Buzz claims to use algorithms to sort out what is most relevant, but I don't have enough friends posting content to verify this claimTwitter has tags, but they aren't used for filteringTwitter isn't designed to make it easy for someone to publish into multiple lists, which might help reduce some of the noise problemI know that some of the Twitter clients probably deal with some of these issue, but features tend to work better when they are part of the main site, rather than just bolted on.EDIT: It has been commented that Twitter isn't designed for conversations, but to let you see what somebody is thinking. That makes sense and I suppose it does this well and explains why it is so poor for conversations.
Alternatives to Twitter
twitter;webapp rec;status
I think you might be trying to bend Twitter into something it isn't.Twitter is a service where you can push 140 character tidbits of what's on your mind/wha'cha doing to the rest of the world... and in return, you can follow what others are up to.Twitter solved a bunch of things...I want to publish/share something (e.g. a cool link), but I don't want/need to create a blog post for itI think that the rest of the world cares about everything I do, thus I must publicize mindless dribble like: I feel like tacos for lunchI want to promote/syndicate my company/event news/products/info to the masses and my SEO expert tells me this is how I should do itI have a mobile device & time to waste - what can I do?IMHO The reality is, that the Internet will really only support 1 (one) of these types of services because the users that are following will only want one consolidated view.  That said, the Twitter API is fairly robust and thus there are a zillion clients out there that can filter, group, sort and manage all the Twitter content you can handle.Finally you mentioned conversations.  AFAIK, conversations are best done with IM (e.g. MSN, ICQ, Gtalk, AIM, !Y, or IRC (for groups)), Facebook chat, or Google Wave (for collaboration)... and/or SMS on mobile phones.FYI: If you just want to track a Twitter conversation between 2 parties, bettween.com offers a unique view for this. e.g. here is the current 'conversation' between @KevinRose/@AlexAlbrecht.