Mountain Lion is not as bad as Lion, but I would wait 6 months...
Whatever you do make sure you have a fallback strategy if you upgrade...I experienced serious problems with both upgrade and Time Machine recovery on ML.
First, I have to admit that I've been using Macs exclusively since I got my first one with System 7 more than 20 years ago. OS upgrades used to be exciting, and I almost always upgraded to the latest release within a week of release.
Things are different now.
I got a new iMac with Lion a while back and ended up downgrading it back to SL. On top of the well know UI and other downgrades from SL there were serious stability problems.
The day after ML came out I did something really stupid and tried an in place upgrade of my MBP to ML. The upgrade process went well except my more than 3,000 notes did not carry over from SL. I ended up going back to a copy of SL and doing a migration upgrade to Lion and then to ML. This time everything worked fine with the upgrade. I had to change a bunch of Apple defaults like everyone else, but to be honest, it was kind of refreshing to use a new OS after so long without a change. ML was much more stable than Lion, but I was still having more frequent MS app and MacOS problems than I did with SL.
Now, the fun part. This Monday I had my system disk die. That was a bummer, but fortunately I had a Time Machine backup from earlier in the day. So, I boot into the recovery partition and restore from Time Machine. Only problem is that this time Mail was unable to restore any of my local mail boxes (I have about 300,000 messages and got a message about "running out of space" before stopping -- even though I had 125GB available. In addition to the Mail problem, there were problems with missing fonts. Apparently, there are still quite a few bugs in Time Machine for Mountain Lion and who knows what else I might discover as time went on.
Fortunately, I still had my trusty old Snow Leopard image on a separate partition. I decided to do another Mountain Lion Install and migrate from that partition. However, I knew that I was going to lose a bunch of recent notes that I created in Mountain Lion, so I copied all of my ON MY MAC notes to iCloud. I even tested to ensure that I could move them back. I also copied a bunch of recent documents to a thumb drive to restore later as well. So, I spent forever doing the install and migration and in the end everything was working -- except I couldn't get my notes back to ON MY MAC.
The Time Machine failure should have been the last straw for me, since I use my MBP for work -- but the iCloud notes bug took it over the top for me.
So, today I am back on Snow Leopard and will stay here for another six months of so until Apple shakes the bugs out of the ML upgrade and Time Machine Recovery processes. I really don't miss any of the ML stuff.
For anybody else thinking of going back to SL from ML it was fairly painless. Here are a few pointers:
- I was able to archive email boxes in Mountain Lion and import them into Snow Leopard with no problem.
- If you keep around a mountable ML partition you can easily move documents back to your SL disk using the SL finder.
- Moving notes was a not as bad as I though. I simply "shared/emailed" all the new notes in ML to myself. I had to do one Note at a time which was a bit of a drag though. However, from SL you just drag the email messages into the Notes and they are fully usable. I did go and copy them one by one into real notes, but I'm not sure that that is really necessary.