Here's what my messages inbox looks like:

Note that links to forum topics are highlighted ("Snap! Team development discussion, vol. 2" is highlighted, for example), but links to users just following you aren't ("Minty-And-Fresh" isn't highlighted). So it's not as obvious that I can click on the username to see who followed me, and it's less likely for me to notice the message at all, because it doesn't have a contrasting link in it.
/cc @mewtaylor
@towerofnix could you please provide your OS type (i.e. Mac OSX 10.12, Windows 10, etc.) and browser version (i.e. Chrome 60, Firefox 52, etc.)? Generally we find this kind of thing helpful when looking at bugs for reproducibility – check out our reporting bugs page for some more info on this.
The reason I ask in this particular case is because it appears that this might be OS-specific, because I am unable to reproduce in Firefox or Chrome on Mac OSX 10.12.
Ah, yep, sorry for forgetting!
I'm running Firefox 52.3.0 on Debian Testing.
I took a look at the new messages page on different browsers and systems (Safari on macOS and iOS), and saw some interesting results:
It looks like Firefox (Debian) displays font-weight: 500 the same as font-weight: 300 (while other browsers display 500 as more bolded).
The default font (no font-family set) does not display font-weight 500 differently from 300:

The font sans-serif does display 500 differently:

The font Arial does not display 500 differently:

The font Helvetica does not display 500 differently:

The font Helvetica Neue is not installed.
This means that the font Helvetica is being used, and on my system (Firefox / Debian Testing), Helvetica is not displayed as bold with font weight 500.
@towerofnix awesome, this is super helpful :).
Seems to happen with any name on the messages page.

Another screenshot taken on a Mac OS X Chrome 46 (old I know but I'm on a school pc)
@rschamp @thisandagain I propose we close this in favor of #1630.
Closing per #1630.
Most helpful comment
Seems to happen with any name on the messages page.