There is no doubt that Twitter and Facebook hold the dominant positions in the social web but they can co-exist quite happily as they cater to different markets; other true micro-blogging services just couldn't compete with Twitter not because they weren't as good but because they didn't have enough differentiating features to tempt users away. Creating an account elsewhere is easy, persuading your social circle to do the same and rebuild your network elsewhere is not.
Friendfeed was a geeks paradise providing extensive aggregation and allowing for in depth conversations without the restrictions of 140 chracaters. It unfortunately lost steam due to the buyout by Facebook and little (if anything) has changed since. Personally, I see Google Buzz as a direct replacement for Friendfeed. As I have said before, the feeling at Buzz is very similar to Friendfeed in its early days and this type of site - especially with the resources that Google can potentially throw at it - can also survive as, again, it serves a different demographic from the "big two". It is even preferred if Buzzers do not stream their tweets as the two communities are disctinct and serve different purposes.
Chum.ly is described by Scoble as a "next-generation microblogging service" but I envisage it really as a direct competitor for Buzz. With the functionality on offer it goes beyond the simple status update and becomes more of a "discussion community". Again you are not restricted to the 140 character limit elsewhere so can go in depth. The inteface and user experience is currently in its infancy but the core of functionality is already there and is working well.
Chum.ly already has some nice features to differentiate itself from the competiton. I like the way draft posts are handled; not only are they held within a separate "folder" but also retained in situ in your timeline so that you can see them in the context with which you were writing them, surrounded by other posts. In fact "in context" plays a big part on the site. Replies and comments can be seen "in context" where the whole conversation they relate to is displayed in a separate timeline - although a "top-down" view would be nice so that it is easier to read the thread chronologically.
The developers of Chum.ly are an incredibly welcoming lot who are always on the watch for questions you may have about the service and even keener to hear your feedback. They are also very willing to explain why certain features work as they do and, perhaps, not as you might have expected them to. Google may have the vast resource pool but the guys at Chum.ly have an obvious, and infectious, enthusiasm which can go an incredibly long way.
Will Chum.ly be looking to compete with the likes of Twitter and Facebook or will it be aiming to find that niche that remains to be effectively filled by Buzz? Personally I think it is better suited to the latter. There is an emphasis on integration with the likes of Twitter but you have more control over how that integration operates which can only be a good thing.
I think there are good things ahead for Chum.ly and, with the right direction, it could quickly become a major player.