I am always on the fence between Lightroom and Aperture, but I am also thinking about the future, when new software shows up. Is there any way to export edits made in one of the programs and import it into another? I realize it can be tricky when edit tools differ, but transferring the standard RAW edits would be a good start.
Unfortunately there's currently no 'painless/seamless/automated' way to make the switch...
What you will have to do to push from Lightroom to Aperture is as follows:
That will get you your RAW files, IPTC metadata, star ratings, and color labels. Any flags you have set in Lightroom WILL NOT transfer over. If flags are important to your organization system, then you will want to add keywords in Lightroom before you generate your sidecar files (Flag, NoFlag perhaps) so you can sort on it in Aperture.
The process is more-or-less the same from Aperture to Lightroom:
As you've probably already guessed, you will not be able to pull files in either direction with edits intact. Your best bet will be to export anything you've made adjustments to as a 16 bit TIFF and then import them into your new chosen application. Again, by keywording the files before you generate sidecar files (Adjusted, or Modified, perhaps) you will at least be able to sort them by keyword once you've got them in Aperture or Lightroom.
Obviously there's no way to know what products will be released in the future that have the potential to make the transition more seamless, but speaking as someone who spent a number of years in the software industry 'in another life,' my personal opinion is that I wouldn't hold my breath waiting, 'cause you will likely never see this transition be made any easier by either Adobe, or Apple... It's just not in either company's best interest or bottom line to make it easy to shift to a competing product, so there's just no real incentive to spend a lot of development time there...