I did not have integration, and I'm sure you are already googled, but ...
http://nosql.mypopescu.com/post/383437318/integrating-mongodb-with-solr
http://blog.knuthaugen.no/2010/04/cooking-with-mongodb-and-solr.html
The problem you are likely to encounter with the psuedo real-time solution, depending on your size, is performance. High-latch Solr performance isn't the biggest. In other words, this is actually not a lot of real-time indexing solutions, as it is a batch indexing solution. Depending on what you are actually doing, this may or may not be a problem for you.
ElasticSearch (mentioned above) has been causing a lot of buzz in the blogosphere lately and it has a JSON api, so you might want to look at it if you use MongoDB. I came across these performance metrics while doing some real-time commit research (although I never used ElasticSearch).
AFAIK, there is only one (very dedicated) ElasticSearch contributor.
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