Glassdoor is widely used in the US but to what extent is it reliable and of use in the UK and elsewhere... 

If you are an employer there are some clear issues. Glassdoor doesn't seem to have basic algorithms to check that the reviewer is based in the same country as the employer. This is an issue for companies who have the same name because employees can select the wrong company and post a review, good or bad.  Our company Aspire has been reviewed as a dentist in the USA and a software company in India. The trouble is even when the employer flags it as clearly incorrect Glassdoor are very slow to react or in one case refused to remove a review that clearly was not about a digital, media and marketing communications recruitment business. 

Overall the concept is great and gives real insight but Glassdoor has to up their investment in oversight in the same way Facebook and Google have belatedly realised that they are publishers and responsible for their platforms content.