First-up, apologies if I'm missing a tongue-in-cheek element to the OP (that chesire-cat grin smiley always throws me), but this is more directed at some of the later posts anyway.
There's 2 different categories of blokes to consider here
a) Blokes being dragged along by the gf, whinging and moaning
b) Blokes with their gf having fun
Nothing to be said for A, but I think B is to be heartily encouraged. It's great when something so widely depicted in the media as being an immutable point of conflict between men and women (clothes shopping) can be used for bonding instead. Couples clothes shopping is great fun, and it's sexy and flattering to have your oh giving considered suggestion on what he thinks you'd look good in, (even if some of his ideas are to be chuckled away)
I don't think a bloke looks "weird" standing inside a women's section, I think he looks far more weird standing awkwardly outside a shop peering fearfully into its feminine recesses as he waits for his gf (but not going in to find her or anything, cos that might look weird. He'd rather just stand in the doorframe mutely waving his arms frantically to get her attention instead, like a normal person)
If you want to find men's presence weird that's up to you, but YABU imo if you mix it with a sense of grievance or entitlement (like the slightly indignant tone about them loudly expressing their opinions suggests), as there is nothing that gives you greater right to the area than men. It's a public shop. You have your own personal concept of how you would ideally like the place to be, and while I find it as disagreeable as that of a bloke who doesn't like girls going to football matches, it's fine if you keep it to yourself. But the onus is entirely on you to find the places and times where you can shop without any men around, if that's what you insist on.
Obviously if there's any inappropriate behaviour/perving then that's not tolerable and is a completely different matter, but I think the vast majority of blokes in women's depts are just having fun with their partner really (or are the afore-mentioned captives). Don't see the problem with men being in the vicinity of changing areas, if the curtain is too flimsy then that's a problem anyway. It should always be possible to clothes shop without feeling any sense of exposure, regardless of the clientele.
Most blokes are very self-conscious and low-key in these places anyway because they're well aware of attitudes like many in this thread and can sense the disapproving vibes. This is why some blokes are ashamed to buy sexy lingerie for their partners (which to many women is the very funnest of gift genres to recieve). This kind of attitude, that women's places are to be regarded as impenetrable unspoiled girly sanctums by self-respecting males only leads to greater patronisation of women, and also plays right into the hands of misogynistic blokes who also find it "weird" to see a bloke going to a girl's place with his OH and would very much like to shame their peers out of it into instead being "a man's man" down the pub laughing about their partner's silly little shopping habits with them.
Sorry for rambling on, and I hope this doesn't read aggressively, because I can sort of see where some posters are coming from, instinctively. But I think it's ultimately divisive to go with these instincts here. Love the site