It seems that us PR people are taking to Twitter like ducks to water. I don't have a number but I'd assume there are potentially tens of thousands of us around the world using Twitter for client initiatives and to build relationships with our peers and journalists. Back in November 2008 (long time in internet months) I actually carried out a little research to see which UK PR people are using Twitter. The response was positive and it was then developed into a wiki. Side note: you should add your Twitter profile to it if you're not already on.
That said, even the wiki isn't a full representation of all the PR people on Twitter so if you're looking to follow more of your peers on the popular micro-blogging platform I have a handy little tip for you which I found on the blog, Mr Google Alerts.
Searching on Google is easy and we all know how to do it. However, with Google search you can also perform comprehensive and detailed search queries making your search very specific. In this case we can tell Google we want to find all the people on Twitter who work in PR and are based in London. To do this we write this in the search box: intext:"bio * pr" intext:"location * london" site:twitter.com
And there you have it. Take a look for yourself. There is a caveat however - the search results will only bring up the people who have specified that they work in PR and are based in London in the 'bio' and 'location' section of their Twitter profile. It's a good first start though and the formula is not restricted to just this. For example, you can also find journalists based in London or Manchester. Or you might be working on an initative which involves accountants, in which case you can make the search more generic to find accountants using Twitter.
The best part is you can add the search query to Google Alerts so whenever a new Twitter profile is added you will get an email from Google notifying you of it.