Personally I am loving the mild weather. I'd rather have wet and mild than freezing cold or worse- snow. We can all still get on with something when its wet but the frost rules out so many gardening jobs.
Without heating in the glasshouse I would have presumed that the plants were a little happier with the mild weather too, but some of our autumn sowings are struggling with the damp air.
If there isn't enough air circulation the can become affected by a fungal presence- botrytis. This appears as a grey 'fluffy' mould and will attack any weak areas. The tender stems of new seedlings are particularly vunerable. Once you see a plant with it your options are to cut out the affected part of the plant (which you can only really do with larger plants) or to just throw the plant out to prevent it spreading. There are probably some fungal sprays out there too but I avoid using things like that unless I really have to.
As with all health matters prevention is often better than cure so, on days when it is above freezing, open all the doors and windows to your glasshouse and get as much air flowing around as possible.