What is most valuable?
In general, I find SharePoint to be a very useful tool when it's configured to allow end users a certain amount of flexibility. (In one of my previous assignments, all options were completely locked down. In that kind of configuration, the usefulness of the tool is highly dependent upon whoever configured the product. In this case, they weren't particularly good.) The latest versions of SharePoint are highly useful for configuring pages for managing and conveying large amounts of information, while giving users the ability to pinpoint the specific things they need with speed and accuracy.
Libraries and lists have a feature set that enables capturing large amounts of information and organizing that information in ways that enable multiple audiences/roles to use it effectively.
How has it helped my organization?
In my previous job, I built a site to support the PMO. It consisted of a top level site that gave a view of all projects undertaken by the organization and then individual project sites that were used to manage issues, risks, changes, action items, key milestones.
The top level site also contained links out to our scheduling software (SmartSheets). The individual project sites were based on a site template, making it very easy to instantiate a new one whenever a new project was introduced. All project information was contained within a single site collection and allowed both broad and deep searches and visibility of key project metrics.
What needs improvement?
I think that the current version of the product is actually quite good, but it's not always easy to find solid training and reference information, especially from Microsoft. Typically, third parties have better offerings than Microsoft, but it still requires a bit of searching to find the most relevant and easily absorbed material.
For how long have I used the solution?
I have used Sharepoint in various forms since around 2003.
Over the last three years (three jobs as well), I've used SharePoint 2007, 2010, and 2013.
What do I think about the stability of the solution?
I have not encountered stability issues with either the on-premise or cloud hosted versions of the product.
What do I think about the scalability of the solution?
I was never involved in planning for scalability, and have never been aware of any scalability issues in any of the places where I've used the product.
How are customer service and technical support?
I generally avoid using Microsoft or Microsoft partner support where possible. Unless you are paying for their top-level consultants (which is frightfully expensive), you're often better off just looking things up on the internet and bookmarking the most helpful sites. In situations where support is being provided by internal staff, the results have been variable.
Which solution did I use previously and why did I switch?
There's nothing truly like SharePoint in the marketplace that I'm aware of. You can use wiki's of various sorts and cobble together any number of open source or paid solutions that address a component of what SharePoint does. But that approach doesn't have the current product's level of integration and the maturity of its feature set.
How was the initial setup?
I don't know about setup. It was never my responsibility. Since the products were in place when I arrived, I don't know who the vendors were that partnered with Microsoft to configure and deploy the product.
What's my experience with pricing, setup cost, and licensing?
It's Microsoft; empty your pockets. Seriously, if you obtain SharePoint under one of their blanket licensing agreements you really need to pay attention to the terms and conditions, especially if your acquisition is part of Office 365. It's typically not very easy to drop licenses for a particular subcomponent under such agreements if you find that you're not using that particular piece.
Which other solutions did I evaluate?
This wasn't my choice. However, there's nothing truly like SharePoint in the marketplace that I'm aware of.
What other advice do I have?
Know what you want it for first. Talk to other businesses using the product to understand their experiences. If it looks like SharePoint can bring real business value, then find the best implementation partner that you can find. I don't know the economic ramifications of cloud vs. on-premise, but I found the cloud version of the product takes a lot of headaches out of your hands with Microsoft being responsible to administer and maintain the back end.
Finally, be very wary of proposals from within your company to build all manner of applications, web sites, and data marts with the tool. Although SharePoint is capable of a lot of things, it may be better to purchase a purpose built product rather than rolling your own.
In the same vein, it is still important to have standards and enforce them within the organization, especially on how sites are structured if they are to be used by people in various roles and departments across the enterprise. Someone has to have a vision for the architecture of your SharePoint installation and use in order to assure you get full value. If folks get to do anything they want, you'll have a crazy quilt of unrelated data, applications, and web pages.
Which version of this solution are you currently using?
2007, 2010, and 2013