I'm interested in comparing the Pro version and the Indie version. I just downloaded 3.3 (haven't installed it yet) and I'd like to be able to do side-by-side comparisons. Can I download Indie directly, or do I have to do the Pro demo download & wait for the 30-day period to expire?
The thing is, you don't download different versions of unity you download different licenses which you 'plug in' to unlock features. Once you download the pro trial licence it's only valid for a month, and I'm sure that deleting the licence and then downloading it again won't work. So the only way you could do it is on two different computers, which then both have a different licence. - I think at least
Here is a nice overview of the differences by the way.
As far as i know you can install Unity into two seperate folders. That way you can access both versions. I'm not sure if the two versions affect eachother (since they share some things like registry keys) but in general it should work. To be on the safe side i would recommend to use two PCs...