Perhaps they mean don't just think that because something has a /24 that means it's a Class C?

Network classes & first octets (for classful networks)
A    0 - 127
B    128 - 191
C    192 - 223

What he said 

This is the only way I can see the comments making sense is if it was served as a warning as opposed to a fact.

Hi Dranex,

Welcome to EthicalHacker.net ! Just incase this helps, I've compiled a decent size list of video links that'll should bring you up to par on Subnetting.

Subnetting in 6 Easy Steps Part 1
http://www.youtube.com/watch?v=wl5_J0UtINg

Subnetting in 6 Easy Steps Part 2
http://www.youtube.com/watch?v=vi1dtaQ1FEo

Subnetting in 6 Easy Steps Part 3
http://www.youtube.com/watch?v=F68dgzY652k

I've uploaded the bottom two that were taken directly from a college class I took called TCP/IP Protocols.

Subnetting Secrets - 26 Bit Mask Example
http://www.youtube.com/watch?v=A9Ica4EfDU8

Subnetting Example
http://www.youtube.com/watch?v=93F1Vbc2ya8

Are you planning on taking the OSCP soon?

Exactly what point do I need to be at before I should be comfortable taking it on with the course materials and research supplementing?

I studied Computing in Uni (Forensics unfortunately, wishing I went down the security route to begin with) so my knowledge of computing is pretty high, most of the stuff we did was with Windows but from a personal geekage point of view I understand Backtrack Linux pretty well now.

I understand networking and the layouts, the OSI model, TCP/IP, Subnetting (thanks to the help you guys left me). I learnt Vivek's Metasploit Megaprimer about a thousand times and read the pentesting with Metasploit book, so i'm pretty comfortable with msf now too.

Is an exploit friendly language the next step or is there somewhere I could better spend my time such as specific exploits, SSH tunneling, SQL injections?

Any help you can give is always greatly appreciated.

(p.s. If you think this question is better off moved to the OSCP specific section I understand)

I know johy come late, but the thing to remember

Classful networking. Class A, B, C, D and E (if I remember them correctly)

CIDR (Classless Inner Domain Routing) you're slashes and subnets. (if I remember correctly)

Back in the 90s, I worked for one of the original six backbone providers. I remember it took two of us, to explain to an ISP the concept of CIDR. They were used to classes, not the classless.

woops  yeah way not ware