According to Distrowatch's hits-per-day ranking system, the top 10 Linux distributions of 2008 thus far are:

1. Ubuntu
2. Mint
3. openSUSE
4. PCLinuxOS
5. Fedora
6. Mandriva
7. Debian
8. Dreamlinux
9. Sabayon
10. Damn Small

I'm more of an underdog fan myself so here's a list of the bottom 10 (of 100 featured in total):

100. DeLi
99. SaxenOS
98. Ark
97. AUSTRUMI
96. IPCop
95. Linux From Scratch
94. Pentoo
93. Ultima
92. GeeXboX
91. Gentoox