I bought a 2GB Sandisk M2 from Renee and nope, it doesn't lag and I have installed 60++ plus of Java games, lots of mp3 songs, ringtones, wallpaper, video clips (movies and music videos) plus my personal pictures too. In fact it's faster than the original Sony M2 because pc magazines have benchmarked the M2 from Sony and Sandisk and they found out that Sandisk is about 15% faster in all benchmarks from uploading or downloading. Of course, Sandisk is way cheaper than Sony. That's the good news. 

may i noe where did ya get ur 2gb m2?
interested in getting one too...
RM150....nice deal   
i wan i wan

there's a warranty to it, right?
one year, if i'm not mistaken
because mine is covered
give the service center a call to double confirm

sheesh
ada warranty card?

by rights, if the faulty product is still under warranty, the manufacturer or whoever should repair or replace it for free
unless, the fault was inflicted by the user ownself, which normally is not covered by the warranty itself
in your case, i still think it's better for you to call or present yourself at the service center directly
enquire a few centers for comparison, too, if you don't mind
just my 2 cents la