If you have reasonable bandwidth between sites, you may also find that you can connect to a remote site without realizing that you're not connected locally.
A warning though: don't take technology at face value, especially when it's the face of a salesman. Bring it in to evaluate your distributed development on your local network. If this is a difficult process in itself, then beware. Test out some real use cases, from all sites. Pay attention to administrative needs, to scalability and to reliability. Force errors and check out the recovery procedures. Load in 10,000 files and see what happens.
There are always going to be issues: very large files across slow links, network outages, etc. But in my experience, distributed development with a single repository and an integrated management suite can be pleasant, and is well within the reach of today's technology.
The measure of success is always going to be: How different is this from a single site scenario?
If you need a recommendation, don't hesitate to ask. I've been using this technology for years and would be more than willing to discuss it with you. Even though I'm biased, that doesn't mean I can't be objective. I'd also welcome your own recommendations and comments as replies to this article.
P.S. Have you taken the time look at the Spotlight Reviews?