Apple has released the latest version of OS X via its Mac App store.
OS 10.8 Mountain Lion is available to buy for £13.99.
The new update adds features including a notification centre, Airplay desktop mirroring and voice dictation.
But soon after release many users complained about errors meaning they could not download the new software.
The Mac App store appeared to buckle under demand as thousands rushed to get the latest version.
Mountain Lion was announced in February, and is described as a move to integrate features of its successful iOS mobile operating system onto desktop computers and laptops.
"People are going to love the new features in Mountain Lion and how easy it is to download and install from the Mac App Store," said Phill Schiller, Apple's senior vice president marketing.
"With iCloud integration, Mountain Lion is even easier to set up, and your important information stays up to date across all your devices so you can keep editing documents, taking notes, creating reminders, and continue conversations whether you started on a Mac, iPhone or iPad."
Reviews have already poured in for the new OS.
"It’s hard to quantify the subjective performance feel of an OS, but Mountain Lion definitely feels faster than Lion and Snow Leopard on the machines I upgraded. It basically flies through tasks, and never really slows down… Ultimately, this is pretty easy: you should spend the $20 and upgrade to Mountain Lion, especially if you have a newer Mac. You’ll gain a handful of must-have features, and everything will get faster and smoother."
In a frankly absurd 27,000 word review, The Next Web said:
"OS X 10.8 is a generous helping of iOS-friendly syncing apps and services, with a sidebar of unfortunately poor Messages and a grab bag of ‘most wanted’ features and tweaks to Lion. It’s absolutely worth the $20 price tag to upgrade, as there is more good here than bad, and that’s super cheap."
"Mountain Lion, and the incremental approach Apple has taken with recent OS X updates, highlights the growing schism between Apple’s and Microsoft’s philosophies. ... That mindset and development schedule — “What can we do to make this nicer by next year?” — may well be the most important thing from iOS that Apple has taken back to the Mac.."
But Pocketgamer said that Apple's love of "real world" textures and making its Apps look like physical objects was increasingly frustrating:
"Grumbles we have however are Apple’s insistence on being “cutesy”. On making things hark back to the last century, which is strange, considering all the features OS X Mountain Lion provides are so cutting edge."
More to follow.