I use them both together just about everyday. I also run Aperture with referenced masters. I take photos everyday of the week. Sometimes I may only take 1 or 2, and other days I might take a few hundred. I've been using Photo Mechanic along with Aperture since Oct 2009.
Here's what I do:
When I get home, I put my card in a card reader, Photo Mechanic pops up. I select one my saved saved IPTC Notepad templates and let Photo Mechanic copy the images to my hard drive. Once thats complete, I quickly sort through the photos, deleting the ones I don't want. Then I add photo specific metadata and ratings to all the remaining photos. Then I geotag all my photos from within Photo Mechanic. Once I've done all that, I import into Aperture for editing/printing/publishing/sharing.
I make very heavy use of keywords and other IPTC metadata. I have yet to find a better, faster way to do all that than with Photo Mechanic. I do almost all my metadata editing in Photo Mechanic. Another great thing to add to this mix is TextExpander. I created snippets for all my most used keywords and other metadata. Now I just have to type something like ,val and it gets expanded to valentines day. This makes key-wording very fast and cuts down on spelling errors.
The only issue I've come across is if I import some photos into Aperture, geotag them in Photo Mechanic, go back to Aperture and tell it to re-read the metadata from the master, it doesn't pick up the new geo data.
I say download the trial version and give it a go. Make sure to play around with the IPTC Stationary Pad.
