I've just installed Build 10049, which introduces the Spartan web browser.

Not sure if anyone else has tried it yet, but aside from a couple of hiccups whilst trying to find the latest Visual Studio preview, it does seem rather good.

Not sure how effective the notes feature, (you can draw notes onto any web page) is going to be, unless you have a stylus/pen, as it just looked rubbish when I tried writing, using my mouse.

Erm, Microsoft explicitly said that 10049 doesn't work with Visual Studio and beta testers who are also developing should move to the slower release ring and avoid 10049.

• After logging in, you may see a blue screen instead of your desktop. To work around this issue, lock your PC (with the hardware button or by pressing the Windows Key + L) and try logging in again. You can also try Ctrl + Shift + Esc to open Task Manager.
• Indexing of new email in Outlook is not working, so search results will be limited to when the last index was built.
• UPDATE: You cannot enable Hyper-V on this build. If you have Hyper-V already enabled and you upgrade to this build, Hyper-V will continue to work. If you have Virtual Machines hosted in Hyper-V on your PC running Windows 10, you will want to move to the Slow ring and wait for the next build as this build breaks the ability to run VMs.
• There are 2 issues using Visual Studio 2015 preview on this build:
  
  • The emulators will not boot and you won’t be able to deploy a Windows Universal app to the Mobile emulator.
    
  • The XAML designer in VS and Blend will crash when opened.
    
  • If you are a developer using these tools today to develop Windows Universal apps and need this functionality to work – we recommend switching to the Slow ring until we release a patch to fix these issues.

I've reserved a Free copy so fingers crossed.

I know that the upgrade should be free, but what do you mean reserved a free copy?

Yeah, I suspect the 'reservation' is so they have some idea how much data they're going to be shifting on launch day. Free version of Windows has never happened before..

An icon has appeared at the bottom right hand corner of my task bar offering to reserve me a free upgrade. 3Gb download so my 37Mb bandwidth might actually have a use.

Worst Windows 10 sacrifices: Automatic updates

Not a missing feature, but a change few will welcome. Although the Pro and Enterprise editions of Widows 10 will both give the end user or network admin the opportunity to decide when updates are installed, Windows 10 Home users have no control. Windows Updates will be downloaded and installed automatically as soon as they're available. This is a classic Microsoft move: it probably makes sense for the entire herd to be immune from security flaws, but end users will not like being forced to install updates at Microsoft's will.

We will reserve judgment until we see how it works, but for now we will say that the idea of automiatic Windows Updates sounds like a recipe for horror and disaster!