I like this question, mainly because everything is subjective. For example, I have Comcast and using www.speedtest.net
I get readings (using the closest server to me and I get 25mbps download and just over 5mbps upload, which HIGHLY exceeds the numbers that Comcast guarantees (using their BOOST PLAN, another $10 a month) speeds of only 16mbps download. I actually got the Boost for 3 free months, saw no speed difference and just have regular Comcast.
In my case, I had all new cable totally replace the development (about 200 homes) where I am and it has been a wonderful experience hands down.
Now the subjective part. What can you realistically do with 25 megabytes per second??... well, there is NO streaming HD movie or TV content that is available through Youtube or Fancast or Xfinity or any service that I can not stream FLAWLESSLY without any buffering. The GREAT part about that is Xfinity (a company that for all intent and purpose IS Comcast) streams HD content in 1080P resolution, although their cable programming is only 1080I a noticeable difference for us videofiles. So, ideally, if you can wait an extra day and quality of a particular program is of great importance, wait for Fancast or Xfinity to have it available and watch it there, the resolution is 1080P which is as good as it gets - basically the standard for all HDTVs and it IS the quality that Fios delivers. I believe so does DirectTV.
That being said, you will notice issues with certain file types, such as HQ MP3 audio (917bit sound) which can actually buffer. Many times THAT is an UPLOAD issue from the streamer, more so than a download issue for you, but either way another good example is:
Let's say you are downloading a video at 1.5mbps and you are watching a streaming feed in excess of 480P resolution, chances are that your video you are watching mat buffer. All this is because the numbers you get at Speedtest.net or other data rate sites are defaulted to the closest servers. You have the option at such sites to choose servers all over the world and the more you PING and average out the numbers, the more realistic up/download numbers you will have.
Interestingly though, if you are doing multiple video downloads (any fast file transfer) you can have several going at 1.5mbps and since you aren't "watching the videos, only downloading them) you see these superfast speeds and no obvious buffering. Having multiple videos streaming and viewing though not only is a data download thing, but a video card issue too - now you are into apples and oranges and the math gets muddy.
I will say, I'm never disappointed though, 25mbps is flying, Fios Fiber-optic claims 50mbps and I'd love to try and see what I can get away with at those speeds. It's kinda like having a 500 gig hard drive and then going to a 1.5 terra-drive (3 times bigger) with the 500 gig, you seem to start running out of room if you are a large file collector, but the 1.5 terra-drive seems to never fill up. So a lot is prospective and everything is relative.
I remember back in the golden days of computing, when the only games in town were Compuserve, Prodigy and a few others, there really was no Internet or visual browsers back then, and the only content you had available was from their servers through dialup to you. The speed was 2400 baud (a word not even known by most people under 30) a speed nearly 24 TIMES SLOWER that a 56K modem - and IF you wanted MAX SPEED of 9600 baud (6 time slower than a telephone modem) you paid a $9.95 premium per HOUR - yes per hour. Forgive my math, but that meant at 2400 baud a 4 megapixel image would take 27 hours to download!!!
So, you got some good speed, much better than most people I would think. The next step is to use either DVI or HDMI output from your computer (with a 1 meg video card or better ideally) and connect your computer to a HDTV. That is my setup and my TV is used for all surfing, anything with the powerful desktop and of course all TV including 3D on this 56 inch screen. That is really amazing and I can only wish that happens for anyone who wants an All-in-One Tv/Web experience.
My wife has a netbook (me too but I use mine at work mostly) and I have a 17" HP laptop for those times when we want TV on, but feel like surfing too. It is always cool to see someone on a TV show and can't think of their name, and just 1) flip over to the web on the TV or 2) use either laptop to find out who it is. Often, it becomes a race to see who can find out an answer first.
Enjoy that speed, I love this topic and thought a few examples might help.