If you consider any Laconica service as a straight Twitter replacement then it can be a little difficult to make the switch if your focus is sticking with the rest of the crowd. What you may not realise is that these Laconica sites are not endeavouring to become the next Twitter individually. Heck, even collectively they are not necessarily looking to replace Twitter. Part of the appeal of having an open source platform like Laconica is to be able to create smaller community focussed microblogging services. A very good example of this is the TWiT Army microblogging site which runs on Laconica. Leo Laporte established the TWiT Army site after an interview with Evan Prodromou, one of the creators (or the creator?) of Laconica with the intention of establishing a microblogging service focussed on the TWiT network ands its army of fans. In other words, he created a niche microblogging service.
What came out of that interview was a fascinating possibility. If you use a Laconica-based service like Identi.ca (I am pauljacobson on Identi.ca) you can connect to and follow people using other Laconica-based services. Although the idea isn’t quite to establish a Twitter replacement (although Evan mention there may be a consolidated stream for people who want one and that would be comparable to a general Twitter stream), the power of the Laconica model is that the sites are distributed. You can install Laconica on your own server and run your own microblogging service. Each Laconica service interoperates with the others (they run the same software and use open standards to communicate).
The software is open source and released under the GNU Affero General Public License. That means you can pretty much use it freely provided you comply with the terms of the license. Because the overall system is distributed the whole thing can presumably cope with the kinds of loads Twitter is dealing with easier (any developers want to chime in and correct or support me?). Laconica also runs on PHP which is apparently a good thing too.
Twitter, on the other hand, is a centralised service running on a platform that can’t sustain the number of users using that service. Granted Twitter is getting better at managing the load, it still has outages that frustrate users to no end even though they keep returning. Perhaps an open source, distributed and interoperable system is better than a centralised platform in the long run?