Windows 8 performance issues

One thing which I do find troubling about Windows 8 - which hopefully has been fixed in Windows 8.1 (I have 8.1 installed on one computer but have only used it a few times), is that while a new installation of Windows 8 runs very fast - noticeably faster on older hardware than Windows 7, after installing a few programs I have seen cases where startup is very sluggish with delays and freezes which remind of running Vista with no service packs installed. (Vista usually runs nearly as well as Windows 7 if both SP1 and SP2 are installed).

A good example of this behaviour is on a laptop I recently had to remove a trojan from. The laptop is only a few months old, and came with Windows 8 installed. When it was brand new, Windows 8 ran very fast indeed. However, now it is not nearly as fast, with there being no obvious reason for this. If the computer was running Windows 7, then am certain the computer would still be running fine.

While, I have seen this behaviour on some older computers I've installed Windows 8 on, I was surprised to see this on a newer and much faster computer.

I am wondering if this a common problem, and if upgrading to Windows 8.1 will help.