I love Skype for its most basic function: IM. I've used it for video conferencing, web conferencing, file sharing and more, but as I've moved on to other services for those things, I'll always come to Skype for communicating with fellow workers. Sometimes you need an answer faster than a phone call or email can give you, and Skype offers that level of immediacy.
Communication is Skype's primary function, and it excels. Through no fault of its own, however, it lacks a lot of the flexibility that other communication services provide. File sharing can get problematic and we've had multiple issues with trying to host conferences with people outside the company. Again, I can't really blame Skype for this. Much of the time it's affected by the network of someone/everyone in the party.
Skype is a great, free tool for communicating within your business. Faster and more efficient than email, and allows instantaneous feedback. There are plenty of options that we don't even take advantage of here. Don't write off this excellent tool until you've had time to explore all the areas it can help with.
We use Skype to quickly and efficiently communicate with each other, and to send each other files/media used in our marketing projects and campaigns. Sometimes it takes a bit longer to upload, but I've noticed delivery of assets is a bit faster overall. When you don't have time to wait on an email response, and you can't get through by phone, Skype is an excellent option.