I have used this site a lot to research prospective hosts over the years. I thought I'd feedback some recent experiences of M6.net. I have been with them for 14 months on their Flex plan. The first year went reasonably well given the low cost. The Parallels Plesk panel was slow and I often had to leave things running and do something else while the panel did its thing. Support was average. Things got fixed but in the order of days rather than hours. I put up with these things as it worked for my low-use Windows sites (I have my high-use sites on Linux dedicated server at iWeb - who I do recommend).
This February, M6 decided to migrate to a new server and WebSitePanel. To cut a long story short, the move was a disaster for me. I had some very strange problems with www. not working (despite dns being there for it), stats didn't work on all sites and email addresses had to be set up by hand by their support staff. I spent two weeks too-ing and fro-ing with their support staff asking them to get the stats working, them saying they were fixed when they weren't until I eventually gave up and moved to another provider.