Do you have to pay to upgrade to Unity 3.4 if you have 3.3 Pro, or are they free updates? and if you do have to pay, is it a lot?
it’s a free update, only major updates will cost;
All 3.x updates are free, but there is an additional charge to upgrade to 4.x when it’s released.
Who said that all 3.x. updates are free? The jump to 2.5 was a paid upgrade as well, IIRC.
Update to all “point” release (eg v3.x) are free. Update from 3.x to 4.x will cost extra, depending on versions.
(If I am not wrong) I think upgrading from Unity PRO 3.x to Unity 4.x PRO will be around $650~$750, and $650~$750 as well if you have Unity iOS or Android (basically for every license/platform).
Pretty sure its free between point release.
This was what HiggyB said back in 2009.
http://forum.unity3d.com/threads/35136-Unity-2.5-pro-to-Unity-2.6-pro
Nope, all .x updates have always been free.
–Eric
Minor updates like .1 to .2 to .9 will always be free if you have pro license. But major version like from 2.6 to 3.3 will have to pay an upgrade fee not full amount if you have previous pro license. Basically thats how it works in Unity. 
Cool. Maybe it was because 2.5 made the jump to Unity Free that I got it confused.
That may make me buy a Pro license earlier, thoguh 
Thanks for the clarification.
Er, that was 2.6. 
2.5 was the first version that ran on Windows though.
–Eric
We already stated that my brain doesn’t work today. No need to rub it in 
What exactly is the price of upgrade though? It seems there are a variety of prices reported in the forum.
50% of the original price, unless there’s a sale/promotion going on.
–Eric
Is the 50% update price only on the next highest version or even if you’d skip one release?
Not sure; there have only been two paid updates so far, and I doubt anyone who bought 1.x Pro would have had the patience to wait 3+ years to skip Unity 2 and go for Unity 3 instead.
–Eric