If it were down to me I would probably choose something like this.

Projects
1B's
500M's
250M's
100M's
50M's
25M's
10M's
5M's
2.5M's
1M's
750k's
500k's
250k's
100k's
50k's
25k's
10k's
1k's
Bozos
Gibsons
TeraBoks
Boks
Trigggls
#1 Ranks
Top10 Ranks
Top100 Ranks
Top1000 Ranks
Subprojects
sub1B's
sub500M's
sub250M's
sub100M's
sub50M's
sub25M's
sub10M's
sub5M's
sub2.5M's
sub1M's
sub750k's
sub500k's
sub250k's
sub100k's
sub50k's
sub25k's
sub10k's
sub1k's
SubBozos
subGibsons
subTeraBoks
subBoks
subTrigggls
SubTop10's
SubTop100's
SquarePants
Vaios
Maxwells
TeraMiRB's
MiRB's
Clanks
subClanks

I certainly don't have all of these, and there may even be some I am not yet aware of, but that sequence is probably better and easier for spreadsheeters like me.
BTW I noticed when doing this that there is an inconsistency with the M's in the subprojects some are upper case and others are lower case.
It just occurred to me that if you really wanted to be spreadsheet friendly then having a nice hidden button/link to press which showed a definitive full list of MM's regardless of whether or not you have any, but also showing the users totals where he/she has them would be bliss. I know you like to keep them a secret till they have earned at least one, so the button could be as subtle as a comma or full stop somewhere on the page.
Personally though, I am not convinced the secrecy thing actually works in Boinc's favour though, as I think seeing, for example, a Clank and maybe 1 or 2 SubClanks is a great pat on the back when you first start. Just a thought.
Let me know if I can be of any further help.
Cheers
PS Don't forget about pMiRBs, cMiRBs, SuperDuperBoks, Sub Projects being included in Maxwells, MiRBs and TeraMiRBs, not to mention Prank and Rankem - Just for when you get a minute