I took a DVD-RAM disc created on my DMR-HS2 into CompUSA a couple of months ago and shoved it into every laptop DVD drive I could get to without removing the security bar.
First, to my surprise, squashing random DVD media into laptop DVD drives and messing around with WinDVD and the system device info on WinXP did not get a single salesperson to stop and help me/escort me out of the store. I don't know what it is about me that makes stores think I don't need or want their assistance, but I always seem to get ignored (Unless I walk around flashing my best buy card and looking at the most expensive item in that section of the store - then I might get help).
Secondly, and more on topic - at least 60% of computers on display (based on machines with unique DVD-ROM drive models) could play a DVD-RAM disc without any additional messing around or software.
Not surprisingly, the Toshibas generally had a compatible drive - the HP Pavilion laptops were mixed (My 2yr old n5390 can) and the Sony's either didn't or had their drive in a place where I could not open it without store assistance.
I also found that the majority of the hand held DVD players could NOT read DVD-RAM discs.
If I ever find the piece of paper where I wrote down the machine models and drive models, I'll have to post it (or add it to the database) - but it is well worth taking in some blank media when buying a laptop to see what it can play (if you plan on using DVD-Rs or DVD-RAM)