SOLVED: Turns out the people not being able to access TFS via VS2010 were using laptops, I didn’t put two and two together, and Symantec Endpoint was blocking the ports required.
Some users cannot get to the TFS 2010 server, secured by SSL, from team explorer but can via IE.
For example, I go into VS2010 SP1 and attempt to add a new server, it sits there for a while and then spits out a dialog that basically tells me “Unable to connect to the remote server”. If I enter the exact same URL into IE I get access perfectly.
So
https://tfserver:8088/tfs (custom SSL port number) in IE and I get full access
The same detail entered into the add server results in
Any ideas?

Connect to tfspreview through VS2010, you need to install following things :
VS SP1: http://www.microsoft.com/download/en/details.aspx?id=23691
KB2581206: http://connect.microsoft.com/VisualStudio/Downloads/DownloadDetails.aspx?DownloadID=39070
Edit: These links are no longer available. The update is now only provided through windows update. See here
KB2662296: http://support.microsoft.com/kb/2662296