incrament saving + autobak every 10 minutes with 8 bak files. plus ctr+s often enough. While photoshop is kinda reliable, 3dsmax is terrbily buggy sometimes. Especially when it comes to import obj files from zbrush. Argh. Downtimes and crashes....
I usually save every 10-15min, and each time I do, I'll check the file into the server. At home, I have 2 external 120GB drives, so I make multiple versions of each file. When the file is finalized, I'll go back and delete the 'working' files, and keep the final.