The pain points with mobile sites has been expressed time and time again via Twitter, now it's time for a little rant in more than 140 characters.
As a web developer I help build and consume a lot of web content. Most of the building happens on an Ubuntu desktop with three large screens. Most of the consuming happens on a phone with a 3.5 inch screen. Therefore a website optimized for a small screen is a really useful idea, although 90% of sites seem to have done this really badly.
The most recent example is with the UK mobile phone store Phone4u, as a website that prime goal is to market and sell mobile phones you would think their mobile experience would be pretty great, in fact it's awful.
The above tweet appeared in my feed last night as a promoted tweet (advert) while I was checking Twitter on my phone. As the Sony Z1 had just been announced hours early I was interested in the pricing. Clicking the link opened a browser window within the Twitter iPhone app and took me too... http://m.phones4u.co.uk/, the "mobile site" homepage, rather than the actual link clicked. Not being defeated by this serious failure I clicked the "coming soon" link, the Sony Z1 was not listed there. Going back I tried the "pay monthly deals" link, the Sony Z1 was not there either. The final solution was to click a tiny little "full site" link at the bottom to get the "desktop site" where there was a banner image promoting the Sony Z1.
All in all, for my particular use case, this makes the mobile site completely useless. The same annoyance would then be expected for many others who clicked the link in the promoted tweet.
Following on with the theme of sites to market mobile phones having a poor mobile experience, uswitch. http://m.uswitch.com/mobiles/ is the mobile version of http://www.uswitch.com/mobiles/. It is lacking a lot of the functionality, features and filters when searching that the main site has. It's another example of where I had to find the "full site" link in the footer to get the desired experience.
Generally desktop sites are okay on mobile devices, like users know how to scroll, they now also know how to zoom. Although if you do want to put in the effort to build a mobile friendly site make sure all the paths are the same so links work, and make sure all the content is there. The best option here is to use media queries, which will allow the content to be displayed in a different way whether it be a phone, tablet, small display laptop or large display desktop.