There *is* a gender-neutral or masculine 〜わ. I still remember the first time I heard it about 20 years ago since I was so shocked to hear a guy use a supposedly feminine ending-wa. But this is actually not feminine at all. As I encountered it, it's used when taking action particularly after making a decision to take action. Like そうするわ which kind of has the meaning of そうしてみます.
Part of the confusion here is that there isn't just a single use for わ. If I may borrow from an online dictionary (dictionary.goo.ne.jp)... The two that apply here (with my translations added) are: (1)（女性用語として）話し手の主張や決意を、表現をやわらげて軽く言い表す。 - (as feminine language) Softens presentation and expresses the speaker's assertion, determination, etc., mildly. ex: 「おもしろいわね」 - "How interesting" (2)軽い詠嘆や驚きなどの気持ちを表す。 - Expresses mild feelings of admiration, surprise, etc. ex: 「これは驚いたわ」 - "This's a surprise" Note that only the first is marked as feminine. And to partially answer chaser48's question, 〜よ (see [yo]) is a gender-neutral way to add emphasis, though it's not quite equivalent, and may even appear alongside わ as in #671.
A few notes from the trenches are in order. :) Out here in Nagoya, you will hear men use "wa" *very* rarely. It's still an oddity such that as someone learning Japanese, you're best off just leaving it alone. Previous posters are right - it's not heard much from women anymore either. When you do, it's mostly middle-aged women who are affecting an air of sophistication; but much older than middle-aged, and "kashira" seems much more prevalent. The good news for a Japanese-learner is that 'wa' is simple: You understand that it's just flavorful emphasis, it's at the end of a sentence so it won't throw you off, and then you never ever use it and you'll be fine. I don't think Miki is fully correct, though, about あれ・あら. At the very least, it varies based on dialect and is not a universal thing. I hear a lot of elderly men who speak Nagoya-ben and Mikawa-ben use "Ara" rather than "are" - either as a drawn-out "Araaaa.." or a quick repetition of "Ara-ara-ara" naturally depending on circumstance. It's not a strong "ra" sound, though, maybe halfway between "ara" and "are"? Just a subtlety thing. If you split the difference between the two, you should be fine. ;)
kansai-ben and aichi-ben (because both mikawa-ben and nagoya-ben use it) use it. on a side note, i said わ once, and all my friends (japanese girls obviously) said i sounded like sailor moon. actually, most owmen i encounter say its not used much, and ive only ever heard outside from tv once after じゃない
Your female friend must be young like early 20s or younger. I would say she is 口が悪い. For mens' use, please change あら to あれ in ex4771.
Yes, she is not exactly a lady... When speaking 標準語 in Tokyo, 〜わ is only used for women. But this is not the case in some other parts of Japan. If you watch Japanese TV, you will often see men from other parts of Japan (関西?) use わ.
In the above examples, if you just leave out the わ they are acceptable for men to use. In Tokyo, the only time I hear young women say this is when they are impersonating older women or in TV dramas. Many people say womens Japanese is becoming more like mens. My (Female) friend likes to call herself 俺!
Then what is the counter part masculine form of 〜わ ?
end of grammar topic
topic updated: this is mostly a feminine phrase/sentence ending, as per miki's contribution. i (as a guy) once used it and was corrected.