So, this is a neat idea, but the way css is designed (i.e. half-leading model) makes generalized baseline alignments
completely horrid because you end up doing all these positioning gimmicks based on the exact descender depth of the font you're using. At that point, you're really designing for the
font which sort of defeats the generality/convenience of css.
I don't think at the time it was designed there was a sense that anybody would actually want features like actual baseline alignment (i mean, look at the extent of UILabel's typography options for a good example of this sort of present-day rationalization) I've nearly given up on having any semblance of generalized baseline alignment in css like i do in, say, indesign, which although horrid, at least got that part right.
That said, if you want a good argument against a strict baseline grid i'll supply one and a half: derek birdsall1's notes on book design[1] and mine:
When i started working through my mfa i had completely drunk the grid kool-aid from Samsara, Elam, Bringhurst and (natürlich) Müller-B. I was obsessed with vertical grids and i used them much to my detriment (because i was blindly plugging away). My shit looked mechanical which is not really me at all. Then i met another designer who said, in passing: "who really uses grids? You make shit look good. When you're done, you tidy it up with a grid if the spirit moves you.* It'll probably already be on some grid, everyone's brain does that, and your post-rationalized grid's practically ready-made. how cool is that?"*
Now, this sort of presumes you can make shit look good which is a tall order, but really it means following your gut and possibly using a grid to keep it in check. If you start with a fixed grid, you limit many of your options from the outset because you're trying to fit stuff into these little squares.
Of course, this takes lots of practice. Practically speaking, grids take much of the choice out of things. If you need to make something that looks cool fast, rip one out of Müller-B and plug away. It will look awesome. Otherwise, loosen up, have some brown liquor and design away until you're happy or trashed or both.
[1]: http://yalepress.yale.edu/yupbooks/book.asp?isbn=97803001034...