Comment 57 for bug 1314556

Ok, I have found a workaround solution, at least for my case - just downgrade the kernel to 3.16 (default version on 14.04 is 3.19). With this kernel lsusb returns result instantly and MTP/ADB work reliably, nautilus shows Android on connect/reconnect immediately, ADB shows device and does not hang etc.

Just click on linux-signed-image-generic-lts-utopic (linux 3.16.0.46.37) package in Synaptic (or sudo apt-get install linux-signed-image-generic-lts-utopic). It should go to grub menu automatically, but one may want to enable showing grub menu during boot like described here http://www.howtogeek.com/196655/how-to-configure-the-grub2-boot-loaders-settings/ . This should not affect installed system, with grub you will be able to choose which kernel to boot.

So, now I have on Ubuntu 14.04 with older kernel 3.16 MTP/ADB work
$ uname -a
Linux anton-hp 3.16.0-46-generic #62~14.04.1-Ubuntu SMP Tue Aug 11 16:27:16 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

On Ubuntu 14.04 with default kernel 3.19 MTP/ADB do NOT work
$ uname -a
Linux anton-hp 3.19.0-26-generic #28~14.04.1-Ubuntu SMP Wed Aug 12 14:09:17 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

OpenSUSE 13.2 live (reported to work in the above post) also has kernel 3.16, by the way.

Another option would be to try newer mainline kernels (did not check them yet):
https://wiki.ubuntu.com/Kernel/MainlineBuilds
http://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D