Some people 'do' Twitter, others like Facebook.
Twitter is increasingly being used for 'instant' comments to other people and organisations.
Just had a useful meeting with a man from https://www.twitter.com/edintravel (http://www.edinburgh.gov.uk/edintravel) who is keen to improve it's information service - esp to cyclists.
Quite a few people here post and/or tweet about bad conditions - weather, ice, potholes etc.
If you put 'warnings' on Twitter consider adding #EdTravCyc