Was reading this debate on Skype:
Skype and five good reasons why you shouldn't cancel your other phone services just yet - The Unofficial Apple Weblog - apple.weblogsinc.com" href="http://apple.weblogsinc.com/entry/7391864753130518/">My gripe with the hype around Skype and five good reasons why you shouldn't cancel your other phone services just yet - The Unofficial Apple Weblog - apple.weblogsinc.com

I posted some comments there as well as Om's blog.

Basically, I think what Skype needs to do next is two-fold
1) change to open standards - i.e. SIP so they can terminate with more service providers and offer better interoperability. Although their architecture may not lend itself to this.
2) Work with hardware vendors, such as Linksys, Netgear, etc. to embed their technology directly in the device. The device can then figure out when dialing if it's a Skype user vs. a PSTN number and route accordingly. This way you can get free call calling when dialing a Skype user and low-cost "VoIP-to-termination provider" (Vonage, Packet8, etc.) when dialing a phone number on the PSTN.