I don't generally use my iPhone jailbroken. But every time I go on vacation of a weekend trip I make sure I jailbreak the phone in advance. I do this to get access to only a very small number of features that really should be part of the OS.
Internet Sharing using MyWi
MyWi does something so simple and obvious. It allows my iPhone to setup a wifi hotspot and share the 3G connection with other devices, i.e. the iPad. That Apple does not provide this feature can only be described as greedy american corporate bullcrap politics. Wether it is to spare ATT from the network congestion, let them sell more data subscriptions or to just try to sell more iPad 3Gs I can't be sure. My opinion of it stands either way since there is no justification for it based on anything like "the users best interest".
Why not just get an iPad 3G? I am not about to get a more expensive AND less pretty iPad 3G just so I can use the 3G connection a few weeks a year. At home or at work I have wifi but, at least in Sweden, we don't generally find wifi hotspots in our rural countryside. Unlike the US, we do have 3G connectivity almost everywhere and Edge everywhere else. And, also unlike the US, we have no carrier restrictions on which device is allowed to take advantage of our mobile data connection.
The Apple-approved alternative is to carry along my Macbook pro simply to act as a Wifi hotspot for the iPad by... sharing the iPhone's 3G connection. Same result but more weight, power, bulk and complexity. Since using the iPhone as a modem for my Macbook pro is available, why not for the iPad? If not via wifi, how about a dock-to-dock cable or something? Maybe they just like me to lugg around all my Apple products :)
Keeping up-to-date with my podcasts
Podcasts are generally released on a weekly or daily schedule. But, since they are also generally over 20MB I am not allowed to download them to my iPhone without a wifi connection. Again, not a problem when I am at home, but a big problem when I am travelling. Again (again), a nonsensical and arbitrary restriction. I can understand a warning. But with so many "unlimited" dataplans for the iPhone and so many other types of data (YouTube anyone?) that exceed this limit I can't understand the restriction. Fortunately, in Cydia I can buy and install "3G Unrestrictor" which does exactly what you'd expect. It removes the restrictions related to the mobile connection.
That is all. The iPhone is that close to being more or less prefect. Two "missing" features that I believe are the cause of the network situation closer to Cupertino (more Wifi than 3G coverage one is almost lead to believe) and splash of arrogance and excessive greed. Neither feature is a deal breaker most of the time but both make my life a small hell when I am away for a week or two.
There is of-course annoying things like complicated file transfer setups and other design decisions that cause problems once you start wanting to actually transfer information in or out of your phone. But those are not so easily solved :)
Also I should note
Well over 90% of the things found in Cydia are crap (my opinion). There are however a very small number of Cydia packages that I actually find useful to have on my phone. A few more are cool in a geeky way but nothing I need on my phone on a daily basis.