The only way I'd consider buying one is if Sony has a way for me to be able to play all of my UMD games on the Go. I'm not re-purchasing the same games I already own.
Since you can just use a regular PSP (which has a bigger screen and it would appear, a more comfortable form factor), which costs less, and has cheaper storage methods available (buy a micro SD adaptor and get up to 16GB or 32GB easily!) to play games purchased on PSN, I really don't see the point, but if the Go gets a bunch of favorable impressions and a UMD solution is found, sure, I might bite.