Not only since I bought the Nexus S, I'm storing all my contact data in Google Contacts. I also synced my iPhone with it. Over the years a lot of data has accumulated there and one thing that always bugged me was how the phone numbers where all formatted differently. Some had a country prefix, others didn't. There where numbers using dashes, dots or spaces to separate the area code…
Not only does it look like a mess, it may also hinder caller identification or calling might not even work.
The result is the Google Contacts Phone Number fixer.
It will add country codes, remove special chars and even knows about area prefixes of a few European countries.
You can try it without risk, it will only apply the changes once you say so.
It's currently heavily tailored to what I like the phone numbers to look like. And it was only really tested in Chrome. I guess it will work in Firefox but have my doubt on other Browsers .
If like it, you're welcome - if you don't, just send patches.