VOIP products are certainly maturing.
I don't have any technical experience with them - although I am a telecom professional.
Here's a couple of personal observations, use a cable modem or dsl line at home and it works great and saves $$$$ - a close friend does this for his home office and the quality is excellent. remember cable modems are a shared bus architecture so there is a chance of contention but if your cable company does it right, you shouldn't have a problem. dsl with guaranteed bandwidth would eliminate any issues there.
on the other hand, a former company used VOIP for its pbx and there were always problems, I don't the specifics (manufacturer/model/software) but it never seemed ready for prime time. I talk with a friend who works for a (the)leader in IP networking products and their office system sounds crappy sometimes - echo suppression/correction just not doing the job & higher level service features fail frequently