My external drives are all FW, so it's not really a fair comparison. It is slower, but not unbearable. I used to have a 2.5" FW portable, but it was only 40 GB. You can still get FW portables but they are hard to come by now and the price tends to be higher.
Doing a quick search, the only new one I could find was from Lacie (a long time apple supporter) Here's a link:
http://www.lacie.com/ca/products/product.htm?pid=10976
This 120 GB retails for $140 although you may be able to find a street price lower. That is the same price as Costco charges for the 250 GB WD passport, so it becomes a price/performance thing.