If you capture your HDV from the camera or deck using Final Cut Studio, the MPEG-2 data will be losslessly wrapped in a Quicktime wrapper in realtime, and can be edited natively without any recompression or quality loss. Final Cut Pro supports native MPEG-2 editing without the need for transcoding, but ONLY when the footage is captured by FCS. It cannot import .mpg or .m2t files.

In theory, a 3rd party could write a program which losslessly takes the MPEG-2 stream out of a .m2t file and re-wraps it in a Quicktime file, the same way Final Cut Studio does it during capture, but sadly no such utility is currently available. The other option is to use MPEGStreamClip and input a .m2t file into the batch and output a .mov file, but keep in mind MPEGStreamClip will perform a recompression and hence loss of quality even if the target codec is MPEG-2.

Unfortunately, iMovie and Final Cut Express don't support MPEG-2 editing at all, they can capture HDV from a camcorder or deck but will transcode it to AIC (Apple Intermediate Codec) in realtime during capture. Only FCS supports native MPEG-2 editing.

Yes, this has been a huge gripe of Mac/HDV users for quite some time now. As long as you capture in FCS it is not a big deal, however for users with a library of .m2t files or who use the Sony hard disk/flash memory HDV recorders, it is a big deal. Unfortunately Apple has given no indication that they are willing to address this problem. On the other hand, if working with .m2t files was so important to you, you probably should do some research about other possible editing systems that will support working natively with .M2T files.