I use the 3M fine line masking tape quite a bit. The blue with orange print is best for a very fine line.
Randy,
By 3M fine line do you mean their blue vinyl stuff? If so I also use that a lot, always keeping the various widths in my "inventory". I use the 3M blue masking with the orange print a ton too, in all widths.
For paint lines though, unless it's a task that requires my using the fine line vinyl, I always use the yellow Frogtape anymore. It's become my new favorite, even over the blue/orange masking. It seems slightly thinner (maybe?) than the blue/orange tape and I feel like it leaves an even better edge. The tackiness is also pretty much ideal, all in all it's very user friendly.