Over the past few days, I’ve read the early Mountain Lion chatter on online message boards, including Apple’s own support discussions. With millions of Mac users already using OS 10.8 — one report suggested the number exceeded 3% of the Mac user base after the first two days — it’s quite clear that some people are going to encounter problems. The key is whether there is a trend towards serious, repeatable bugs that may indicate potential troubles with Mountain Lion that Apple will need to address in the first maintenance update.
After installing Mountain Lion on a late 2009 27-inch iMac, and a 2010 17-inch MacBook Pro, I can tell you that my upgrade experiences have been quite smooth. I can think of only two problems after the installation, one of which appears to have been encountered by others.
The first involved high resource use by Mountain Lion on the iMac, which slowed down performance noticeably. Using Apple’s Activity Monitor app, which is found in the Utilities folder, to see what was going wrong, I encountered a process called ABAssistantService hogging the CPU. This process was evidently caused by Contacts constantly polling iCloud for updates.