What make/model of machine is it? Does it come with an Advanced Format/512E drive - if so, have you patched your WinPE boot image and OS? >> http://madluka.wordpress.com/2012/06/12/patch-your-configmgr-boot-image-for-advanced-format-512e-drives/
30-50 minutes is about average for a ConfigMgr OSD deployment I find, including a fully patched OS and some core apps like Office 2010, Java, Citrix, Flash etc. Sub 30 minutes is barely achievable unless you have great hardware, great infrastructure
and a lightweight Task Sequence. One of the reasons ConfigMgr can take a 'little' longer than other solutions is that the ConfigMgr client seems to take AGES to initialise and continue the Task Sequence - this alone seems to add up to 10 minutes to a
deployment - but you have to consider that ConfigMgr is an Enterprise class solution, generally that scales and handles very large numbers of machines very well... small numbers of machines, not so well, in terms of speed - IMHO.
Use the reports to see which steps are taking the longest to run in your Task Sequence - if it is the "Apply Operating System Image" step, then this may be the AF drive thing. If it is Windows Setup, not much you can do there I'm afraid other than
re-evaluate the hardware being used and the drivers.
Andy