I have flown several times with BMI and agree with all that has been siad before. As a quick point of note - you only get miles and tier points for business class from LHR-EDI (and other short flights).
When I took my first flight I phoned BMI directly. I was told by two of their staff that they were NOT a partner of Virgin. I eventually got Virgin to phone up BMI to sort it out - a more senior BMI rep then called back and apologised for the misunderstanding.
I always just use FC card at checkin. However, make sure you keep all reciepts/boarding card stubs etc. About 50% of my BMI flights never appeared on my FC account and I had to send proof - fortunately they all got there in the end

cheers
mcjock