It probably won't affect overall performance very much. You may notice startup time is faster. It does make the PowerBook more quiet, and it produces less heat, so its fans may come on less often (making it even more quiet).
I replaced the hard drive in my even older PowerBook ("Pismo") with solid state storage. First, I used a physically tiny SDXC card (32GB) on an adapter, and that worked surprisingly well. I had previously used that same SDXC card (Sony branded) with my 2011 Mac mini (in its high-speed SD card slot), as an alternate startup disk for testing purposes. The adapter I used is like this one
http://www.amazon.com/Optimal-Shop-Secure-Digital-Adapter/dp/B00BANFDWG
I used it that way for about a year or so. Then, I replaced it with a 128GB mSATA card on a different adapter
http://www.amazon.com/gp/product/B009BA8V4M
The mSATA card (plus adapter) is noticeably faster, when doing things that require concentrated disk access, like when starting up. That makes sense, because an mSATA card (unlike an SD card) is designed to be a computer drive (not media storage). The total cost was about $55, probably even less expensive now. I bought the mSATA card (Samsung branded) on eBay. It was used and the seller had larger number, so I figured they were "pulls" from laptops that were recycled or upgraded to higher storage. 128GB is the maximum for my old PowerBook, so it was a good deal (about $40 at that time).
I posted more info in another similar topic (including a product review for the mSATA adapter), a few months ago...
Re: Solid state hard drives
