If you are currently using an aggregator, want to try Jäger and you it export an OPML blogroll to a web location (i.e. http://...) then you can easily move your subscription list. Just export the OPML blogroll and drag the URL link into Jäger (or do Actions > Add a weblog... and paste in the URL).
This will take several minutes to complete, as a lot of "discovery" has to take place.