podbreak - there are a stack of guys who are well and truly more than half way to the 8 year mark, with absolutely no sign of an FO slot in sight. As an example, the last 767 FO slots (all 3 of them for the whole training year!) went to guys who are around the high 1600's in seniority - meaning they joined in 2000.
However, as a means to ease the pain whilst waiting for an FO slot, earning solid $$$ as a S/O goes a long way I guess... while it lasts