Well, yeah. It all boils down to adding fractions.

5/4 is usually broken down into a 3/4 and a 2/4, or vice versa. 7/4 is often rendered as 4/4 and 3/4, and so on. I usually count a 9/8 to myself just by doing a really slow 3/4 with triplets on each beat.

Getting familiar with weird time signatures--and with music that seamlessly incorporates time changes--makes writing an interesting song so much easier. Perhaps the best example of a writer who incorporates time changes and odd time signatures into very "pop/rock" style music--ie, without calling attention to the time changes, as progressive rock usually does--is Jason Robert Brown. (Particularly "She Cries," "See I'm Smiling," "The Next Ten Minutes," and "Thirteen). Joni Mitchell's later work also does this brilliantlyTechniques such as hemiola are also a great way to switch up rhythms--staying in the same time signature, but articulating and accenting as if you're in another. Nothing really bugs me so much with musicians as when the beat obviously wants to vary and they keep playing straight because they don't know how to do otherwise.

Also, listening to a lot of nice latin music can help--they like to switch between 6/8 and 3/4 a lot ("America" from West Side Story is a perfect example of this). It creates the sense of a constant beat--very danceable music--while still shaking things up enough to keep things interesting.