It's gone. You can edit .mov's or image sequences in Photoshop though or individual frames. But yeah - the filmstrip technique was great for roto work. BTW I think it disappeared after CS3 in Premiere but it's now gone from AE CS5 as well.
Though I have not used it, I also think that PS-Extended has replaced the need for FLN, as it can now work directly with MOV and AVI (obviously, there can be CODEC variations in each, so one would need to be specific on the exact CODEC to choose). That should save a lot of work.