Yes, quite safe but on some sites you may have to log in again. Here's how to delete cookies safely and how to block unwanted cookies:
HOW TO DELETE COOKIES
This is the 'best' way to do it in Internet Explorer 7:
Close IE and Windows Explorer, click on:
Start > Run > type inetcpl.cpl > ENTER
The Internet Properties box will pop up. Click on:
General tab > Browsing history 'Delete...' > Delete Cookies > Yes > Close > OK
In Firefox:
Click on:
Tools > Options > Privacy > Show Cookies > delete individual cookies or all cookies.
CCleaner is a useful free tool for clearing away the minor crap like cookies. Get the SLIM build (no added toolbar) here: http://www.ccleaner.com/download/builds/...
HOW TO CONTROL (BLOCK) COOKIES
In IE7, click on:
'Tools' > 'Options' > 'Privacy' > 'Advanced' > Override automatic cookie handling
Allow First-party cookies and block Third-party cookies. First-party cookies are set by the web site you are actually visiting and some won't work without cookies enabled. Third-party cookies are set by e.g. advertisers on that web site, these are the ones you particularly don't want.
You could set First-party cookies to 'prompt' but you'll probably find it annoying after a short while.
If you're using Firefox, click on:
Tools > Options > Privacy
Accept first-party cookies, don't accept third-party ones, keep until you close Firefox and select to clear private data when you close Firefox.
If you use SpywareBlaster it will ban cookies (and ActiveX) from known bad sites:
http://www.javacoolsoftware.com/spywareblaster.html