Current implementation of tags ajax suggestions (in blogItems, forum post forms) is not usable. It is also reproduced in my case with liferay.com
The thing is - then user started to enter tag in inputBox, ajax request sent immediately and while request sent - inputBox is not accepted user inputs. So, if I know tag name I want to add and starting type it - only first char will be typed - rest will be lost because ajax request are sent.
Suggestion: send ajax request only if user stopped to enter text in inputBox (for example 1-2 seconds delay). Also - I do not think it make sense to send suggestion if only 1-2 chars are entered - so, it looks like it make sense to send it only if 3 and more characters entered