Any issue with running 240v and 120v THHN in the same conduit and can they share a ground?
There should be no problem doing what you want, as long as all the conductors and overcurrent devices are sized properly. As per National Electrical Code, you'll size the equipment grounding conductor (EGC) based on the largest overcurrent device used. Which means the EGC will likely be sized based on the size of the breaker protecting the 240 volt circuit.

National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 250 Grounding and Bonding
250.122 Size of Equipment Grounding Conductors.
(C) Multiple Circuits. Where a single equipment grounding
conductor is run with multiple circuits in the same
raceway, cable, or cable tray, it shall be sized for the largest
overcurrent device protecting conductors in the raceway,
cable, or cable tray. Equipment grounding conductors installed
in cable trays shall meet the minimum requirements
of 392.10(B)(l)(c).