Caching something forever just doesn't impress me at all, it did when I first heard about the rails pipeline, but what matters to me more is that it's cached through a proxy or CDN, and that eTags prevent large files containing the exact same bytes from being sent repeatedly to the same client.

It impresses me as a user though since ETag still incurs a round trip while "forever" expiration doesn't. There's a night and day difference between ETags and no HTTP request at all.

You are likely complacent because you're always on a good connection, since you keep arguing in these comments (even farther down) as if conditional GET requests obsolete other forms of caching.

The real benefit of ETags is that they generalize over all content dynamically, but they come at the cost of incurring more requests than expiration caching. I don't see how you could keep arguing here unless you didn't understand that trade-off.

Another thing to remember: browsers don't fire up unlimited requests, usually you have 6-8 pipes to get your assets through. Even simple if-modified-since will still take space in them, while "eternal caching" will leave them free, i.e. no request will be made.