I saw a few threads in which people wanted to migrate their FogBugz cases into Lighthouse, and while there is no official solution, there are ways to do it, albeit in a limited way.

Basically, you export your FogBugz data to CSV using BugzReport, and then import using csv2lighthouse ruby script.

There is one major limitation: csv2lighthouse only imports three fields (title, description, tags). I want to extend the script, but I have to learn Ruby first, so I'll let you know how that one goes.

A couple of notes -

1) When exporting from FogBugz to CSV using BugzReport, make sure to only choose three columns of data. Choose wisely!
I chose title, last comment, and area.

2) If you absolutely need a fourth column, like the case number, export that column and concatenate with title or some other column in Excel or similiar. As long as your CSV has three columns called title, description, tags, you'll be set.

3) If you've never used Ruby before, or the terminal, don't worry. It's not that hard. Just install Ruby, then install the lighthouse API. Then download csv2lighthouse from GIThub and execute. In case you've never used Ruby before, you need to send the script the CSV document name as a command line argument like this:

csv2lighthouse.rb fogbugz.csv

Only other drawback is BugzReport seems to truncate data kind of randomly when you export. I'm not sure what's going on there, but it's not a huge deal.

So yeah, that's what I did, and now Lighthouse has 5 years worth of issue tracking from FogBugz!