I've got the same problem. JOSM goes out of memory. With both OpenJDK and Sun Java this is happending.
But in fact I am assigning not just some MB - I am assigning some GB. But there is obviously a memory leak.
It might be related to aerial pictures but it might be also a coincidence.
It does not matter which JOSM version I am using. This happens since several months.
Please, open a new ticket and add your system info (see status report). If possible attach an example .osm file. What kind of aerial pictures are you using ? Maybe you could try older versions and find the code change which introduced the leak.