Generally, yes, going from a 160GB to a 250GB will give better performance in laptop drives, but not in desktop drives.
TomsHardware.com has charts to look at for you compare different drives.
However, now that SSD drives are out, I've tested several different models of them. SLC models based on the Samsung drive are unbelievable! FAST!!!! But, drive size is small, 32 or 64GB.
We tried these and LOVE these things:
G-Skill Falcon SSD:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231255
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231221
64MB of cache, not based on the dreaded JMicron controller! These things are GREAT!
I bought one last week and put it in an HP tc4400 tablet PC with 1GB of RAM. XP screams. Windows 7 build 7100 screams, Ubuntu 9.04 screams. Apps load darn near instantaneously in Win7 & Ubuntu (XP strangely takes a bit longer, I think it's a video driver issue). Java apps that take 12-20 seconds with even a fast Seagate 11 or 12 series drive take 2-3 seconds with one of these SSD's.
My suggestion is to find the laptop you like but buy it with the smallest traditional hard drive to save a few $$, then get a G-Skill Falcon drive to replace it. Then you will be a VERY happy camper.