Christopher Painter recently posted an interesting WiX post, WiX: Forced to use Beta Software, and now has a follow up cleverly titled, Pay No Attention To The Bugs Behind the Curtain. These are very good arguments that have been bought up, but I think there is another aspect that is being slightly overlooked. WiX is free open source software.
My experiences with open source projects have generally come with the issues that Christopher has been raising, lack of support, unknown release quality, and unknown version compatibility. If Microsoft and not just their employees, on their own time, built WiX, many of these concerns might go away.
Being open source is also its strength. It is completely free, if you have the time. If WiX were a commercial product, it would then have great difficulty competing against the current major MSI authoring tools. If you come across any showstopper bugs, you can fix them yourself, although this can be a time consuming, expensive process. If it does not suit, you can make it. You just need to look at what SharpDevelop did to the WiX MSBuild target for WiX v2 to support fragments in their IDE. The difference is the developer remains in control. Whenever you use a third party product you are depending on them to support and fix any issues you find in a timely manner. This does not always happen and can leave you stranded.
Being forced to use Beta software is a bit of an embellishment. I completely agree that as a setup developer you are stuck if you want to use Votive. How do I get around this? I do not use it. WiX v2 is great, Votive v2 is not. As long as you can hit a button and create a ready to ship MSI, this is all that matters. I simply have an empty C# project that contains the list of WiX files. In the MSBuild script for the project, I run the command line tools to generate my installer with WiX. I have the WiX release I used to develop that installer, checked in source control, and referenced by the MSBuild task. You do not need to be concerned about what WiX release you are using as long as it creates the MSI you need for your project.
This only becomes an issue when you want to take advantage of new features or you come across a bug that you cannot workaround. Here you have two options. See if it has been fixed in a later release, or fix it yourself. If you use a later release, then you have to go through a complete quality assurance process of your MSI you have created. This is like any commercial product. If you fix it yourself, it will cost you time, but hopefully you will be able to estimate the timeframe that will be required. This is not like any commercial product. For example, we have recently come across a showstopper bug in the .NET Framework 2.0 SP1. This is preventing us moving forward to .NET 3.5. The fix is known, has been raised with Microsoft, but we need to wait for their process to get a fix. (A recent update informs there will not be a hotfix release, because a workaround is available, which may not help to us, because the code is in a 3rd party control.)
I am using WiX v2 and do not intend to move to WiX v3 until the schema is stabilised and it is given the go ahead. It would be too expensive for me to develop my installers in v3 and have to modify them heavily to work in later releases of v3. There are already plenty of modifications required to move from v2 to v3, so I only want to have to do this once. Having all the developers focused on v3 is an issue since support for v2 is short. The mailing list alleviates this issue, although many responses are "you can do this in v3", which is of no help. I would like to move to v3 due to great new features and integration with Visual Studio. This is not something that I can do if business depends on it. It was a risk moving to WiX v2 while it still was not finished. I had to choose a weekly release and work with that, until I hit a bug that was fixed in a later weekly release.
Now that WiX (Votive specifically) is being developed within the Visual Studio Rosario team hopefully releases will be more supported, higher quality and better version compatibility. It is unlikely that I will move to WiX v3 for any commercial project before a release candidate of Rosario is available.