I've been with ING for over a year now. There aren't any catches or anything, I've racked up a couple hundred in interest last year. Their rates consistently beat out just about all banks that I've come across and are generally competitive with even the best local credit union rates. The rates will fluctuate depending on changes to the prime rate, like any standard savings account.
The only downsides (rather minor in my opinion): It generally takes one or two business days for the funds to show up when you transfer money to/from your linked accounts (at least in my experience). And after you move money into ING, you can't touch it for five business days.
Even if you don't have a lot of money to stash away, you can't beat a free $50 for signing up.