The advice from our panel...
Keep it simple, focus on the content and don't worry too much about the delivery mechanism.  Particularly for inhouse meetings it is important that people have a platform to get the information they need.
Plan. Plan. Plan.  Test. Test. Test. Rehearse. Market......It is relatively easy to set up an event, but the planning, testing, rehearsing and marketing of the event is often overlooked.  Just as you wouldn't wing an in-person event, make sure you spend the time preparing and marketing for your online event.
Resource your event appropriately.  Depending on the magnitude of your event it is worth having a production person supporting you - someone who can be a co-host of your webinar, manage the digitial interactions with Q&A, facilitate conversations etc.  The idea is that the presenter or facilitator should be focusing on doing just that, and their should be someone behind the scenes making sure the production all works.