I check my site speed using this tool http://tools.pingdom.com/fpt/
I am getting 2-2.5s load time. Is that fast enough for mobile users?
What has been your experience so far?
Check out caurmen's bangkok STM speech. He talks extensively about that and I think he showed some data correlating page speed and ROI.
It should be anything less than 1 second.
Try to remove picture backgrounds / gradients and replace with CSS.
Also minify all your js / css external files.
Make sure your visual stuff is loaded under a second. For other stuff such as javascript e.t.c. it can be ok if it takes a bit over a second.
I use wordpress and use a plugin called w3 cache to severely reduce loading speeds (homepage loads in 0.5-1 second all across the U.S.). sometimes my loading speed goes to 1.2 or 1.3 seconds, so i think a general rule of thumb is don't let your loading speed cross the 1.5 second threshold.
i'm a coding retard, so i wouldn't be able to do this without wordpress. hope that helps.
Best site to test mobile loading speeds?
...as fast as lightning 
For mobile, there is no such thing as "too fast". I ALWAYS aim to keep lander loading speeds under a second, and under half a second if I can manage it.
Amazon.com has shown that ROI will tend to drop 1% per 100ms of additional load time. That's on desktop. Mobile is more demanding. You also see huge abandonment rates above 2-3 sec.
I did indeed talk about this at Bangkok: http://stmforum.com/forum/showthread...l=1#post150067
@stackman - there's no particularly good site for mobile specifically. I've been waiting for someone to start a loading time test site using 3G, but it hasn't happened. My usual go-to sites are either tools.pingdom.com (for US or EU) or uptrends.org in the "Free Tools" section (for everywhere else).
here you go
http://www.webpagetest.org/
-3G or custom speeds in the dropdown menu
-loads of locations
-replay video of the page being rendered
lol, i didn't notice ricmed's reaction on page 2 
Ideally you would have a real device doing it that has some sort of carrier emulation (rather than bandwidth shaping), and requires an actual device to download/render the page. Some devices can be so slow at loading pages... 1s download but 10s to get there.
Akamai has some mobile page test but it seems quite impractical for the IMer.
I think the best approach is to use Keyote MITE. It's badass to say the least. It emulates devices very well including hardware capabilities e.g. concurrent downloads. Furthermore, it seems you can use part of MITE to throttle connection speeds to simulate real-world bandwidth. Set to say 100 KB/s and optimise for that!
They also offer a "Keynote Mobile Testing" platform that has access to real devices and carriers, though I am unsure if it provides page load speed analysis - definitely check it out as they do have a free version.
I use gtmetrix.com - it's even better