Re: Open source lock-in
It makes no difference if you have spent 5 years building a mission-critical system using open source tools such as PHP, or closed source tools such as .Net. You are still locked-in to that platform, and it will be a major cost to migrate to another platform (regardless of whether it is open source or closed source).
Similarly if you need an ecommerce package you could purchase an open source or closed source package, but after you have spent time and money on training your staff, adding your products, and processing orders - you will be locked-in.
The converse of this is of course that there is no particular advantage to open source vs closed source - open source is simply a good marketing term. The only decision that matters is choosing the platform or package that provides the best fit and best value for your requirements.