When changing tab groups (especially vertical tabs) the transition from one group to another looks very 'unpolished' and 'untidy'.
Finding it hard to come up with the correct word for 'we have totally forgotten to include a smooth transition from one visual state to another'.
Please think about adding a bit of visual polish to this otherwise awesome program, it certainly deserves it.
addendum : on the subject of transitions - more logarythmic - less linear