I'd like to make the case that the way MC auto-refreshes/populates it's smartlists is not ideal for people who use external devices.
MC auto-refreshes the playlists by essentially deleting all tracks and then applying the rule set to the library to re-populate the playlist. This is fine for people using the playlist on their home computer. Hitting the refresh button essentially does the same thing.
iTunes, on the other hand, goes through each song to see if it STILL fits the rule set. If it does, then it keeps the file. If it doesn't, it deletes the track. Once it's done with all the tracks it ONLY re-populates the tracks that it removed, in order to fullfill the limiting rules (e.g., 50 tracks, or 5 GB).
If you are like me, and use smart playlists almost exclusively to pupulate your external device, the difference becomes enormous.
Say you have a 60 GB iPod (or iRiver). I have 5 smart playlists, one for each of my favorite genres (electronic, indie, jazz, etc...). Each is limited to 10GB. In addition to the genre rule, I have rules saying the track cannot have been listened to or skipped in the last 4 days (I sync my pod at least once every 4 days, to pick up new music and grab any new podcasts).
Now, say I've only listened to 50 jazz songs at work. With iTunes smart playlist behavior, this is what happens when I plug in my pod....
iTunes updates the last played stamp on all the files.
iTunes examines the smart playlists, and deletes the 50 Jazz tracks I listened to, replacing them with 50 new ones.
That's it! None of the indie or electronic songs get replaced, assuming I didn't listen to them.
Syncing takes like 3 minutes. My hard drive isn't over-heated. My iPod battery isn't run down. Quick and easy.
Now... with MC, on the other hand, 50GB of stuff gets transferred! Even though I haven't listened to the old stuff. I'm sure you can see the advantage now.
I'd love it if MC could somehow take this into consideration. Perhaps an option could be added (auto-refresh on/off). With auto-refresh off the playlist would act like it does in iTunes. With this option on the functionality would stay the same. Considering it's a simple thing to hit the "refresh" button anyway, you may want to simply reconsider how this works.
Anyway, I want to congratulate you guys on an amazing application! This is my only major issue. I've only been using it a couple of days, but in every other respect it seems far superior to iTunes (and any other manager I've used). It's responsiveness is far better than iTunes with my rather large library, and it only uses 1/2 the memory.
So, this is my plea for you guys to consider adding an option or something to the smart playlists. I'd love to use MC to sync my pod, and leave iTunes behind for good!