I think that the limit of 3 MB to import (fromo WP to WP) must be higher. The base I had now (few months and an average post every 3/4 days) it's about 1.3 MB.
If I keep this track, in about 6 months, I will not be able to import the full base anymore. I think that the import option it's very important to keep our work safe and I don't see why the limit is so little. I've seen blogs that had back ups up to 120 MB... but in case of failure, they won't be able to recover the full blog.