This is what the top of the list of users committed to a proposal looks like:
What is the difference between sorting by total rep and sorting by user rep? Switching between them doesn't seem to change the sort order in a noticeable way, though I haven't examined them particularly closely.
(Thanks for being my guinea pig, Pekka.)
I think that the "total reputation" tab sorts the user basing on the sum of reputation in all the sites where the user has an account (and the reputation is at least 200), while the "user reputation" sort the users basing on the reputation they have in the six sites where their reputation is higher. Users without an account with a reputation of at least 200, or with a single account where their reputation is at least 200, are handled differently.
(The accounts shown in the screenshot are Mohit Bumb, and Simon Hodgson.)
To notice that in the case of, he has more than 2 accounts, and the sum of the reputation on those accounts is higher than 202. This could be explained with cached data that is used to show the flair, but it could also be explained with the fact the flair doesn't show the sum of the reputation on all the sites where the user has an account. Knowing which sites are considered, in this case, is quite difficult; I would expect that Area 51 is always included, but I cannot confirm this.
Taking as example Pearsonartphoto, 29129 is the sum of 10717, 6274, 1482, 1172, and 1137; 31449 is the sum of those six numbers, and the reputation he has in other 13 sites.
Normally, there is no difference between sorting the user using their total reputation, or their user reputation. In some cases, there could be a difference, such as in the following (hypothetical) example:
Site User A User B Site A 20240 20000 Site B 20000 20000 Site C 15000 15240 Site D 12500 12560 Site E 11060 11000 Site F 10000 10000 Site G 0 5600 Site H 0 5800 Site K 0 4800
The total reputation for User A is 88800, while for User B is 105000; the user reputation for both is 88800.
For users that have referred other users, I think the total reputation includes also the reputation of the referred users, such as in this case:
Sorting by "total reputation" includes the reputation scores of anyone the user has referred, whereas "user reputation" includes only the user's own score. If a user hasn't referred anyone else then their total reputation appears to be equal to their user reputation.
kiamlaluno's description of how user reputation is calculated appears to match up with my observations for users that have met the "avid user" 200-point requirement but I haven't looked into that part very closely.
For example, on the SmugMug Answers total reputation list the top listed user is Don MacAskill with a total reputation of 235k. However, Don MacAskill only has a user reputation of 2,776. That matches a sum of his reputation on Area 51 and the sites on which he qualifies as an avid user: Server Fault and Stack Overflow. (Area 51: 1,811 + Server Fault: 621 + Stack Overflow: 344 = 2,776.)
Switching to the SmugMug Answers user reputation list changes the top user listed to hobodave (the #2 user on the total reputation list) who has a reputation score of 35.5k.
