I dry-brush with acrylics all the time. There's a secret weapon that makes this as easy as DB'ing with enamels or oils. It's called (I'm not making this up) - Acrylic Retarder. It's a thin gel available in art stores. You mix it with model acrylics, or, better yet, artist tube/high viscocity acrylics. I usually make a small mix of white artist acrylic, retarder, and the base color of the thing I'm drybrushing. With the retarder in it, you've got a lot of workable time when you can just wipe off any mistakes. But once you leave it for an hour or so, it dries as indelibly as any acrylic.
Here's a link to the retarder:
linkname And note that artists' acrylic tubes are MUCH cheaper for the volume than the little bottles they sell to modelers! One tube of titanium white would DB many hundreds of models, especially when mixed with the retarder!