Which are the most significant features that Microsoft included in Windows 7 SP1? I mean, worth the download, should I waste my time upgrading? I saw on some forums that some users are having problems on booting Windows after upgrade.
Among the enhancements in Windows 7 SP1 is new support for identity, authentication and minor bug fixes that correct audio and printing problems.
For identity, Windows 7 SP1 adds support for a passive profile protocol for use with third-party federation services. The feature adds support for the WS-Federation protocol and enables passive identity requesters such as web browsers to more easily handle subsequent identity tokens such as cookies or custom identification mechanisms.
Other bug fixes address problems with audio and printing. Although a test at eWEEK was unable to demonstrate either the HDMI audio problem or the XPS printer problem. In both the original Windows 7 version and machines with Windows 7 SP 1, we were able to connect HDMI TV monitors to the systems reboot and still have a connection to the device. I was also able to print documents that contained a mix of portrait and landscape pages using the XPS printer driver with no error.
This version of Windows 7 also provides more control over how some features are implemented. For example, it is now possible to change the “Restore previous folders at logon” function that is governed by the Folder Options Explorer dialogue. If this check box is selected, all folders are restored to their previous positions.
In a nod to processor changes and improved security, Windows 7 SP1 now supports AVX (Advanced Vector Extensions). AVX is a 256-bit instruction set that can be used by floating point intensive application performance. With AVX support in Windows 7 SP1, applications can now take advantage of the new instruction set and register extensions.
It's your choice if you want to upgrade, I have successfully installed SP1 on 5 machines without any problems at all. The problems users face are probably due to their other software on the system.
Do you have Windows Update turned on?
If so, then you've probably got most of the features in SP1 already as it is a collection of all the Windows Updates to date (as well as the other new features mentioned by Sandeep). It will also have been offered to you (or already installed - depending on your settings) as it is a Windows Update itself.
If not, then your system is potentially at risk - the exact nature of the risk depending on your actions and what anti-virus (if any) you have installed. This might be the cause of some problems as the service pack will have to download and install all previous updates, but I've not experienced any problems with (an albeit small) sample of machines.
I read that there also are changes on the windows boot up processes, at some phases Microsoft had optimize some characteristic (although I didn't got any visible changes on my system).