I'll agree with you there. The eval is unnecessary.

But 

fn bt {
	eval '{'for {tail -f $i &} '}'
}

mimics how I would write it by hand.

{tail -f file1 &; tail -f file2 &; tail -f file3 &}>file

Which allows me to consider the command one block, which I can pipe to and from etc.

The idiom that you and matt give doesn't work for pipes

tail -f file1 &; tail -f file2 &; tail -f file3 >file

only puts the text from file3 in the pipe. 

The for loop you gave obviates that problem, since it counts as a single block, but it's considerably different than my interactive shell usage and is more verbose(though much more readable :)).

Noah