This may not be helpful as I am in zone6 but I wintersowed ipomopsis 3 years ago and it has "wintersowed" itself each year since. Last winter was relatively mild for us with some snow cover. The plant itself is fine textured and grows to about 18-24 inches tall in my yard. Because of its fine texture, I think you need a good patch of it to show up well.
I think it's worth trying.

I WS'd it last year. I am also in zone 6, the plants grew about the same size as pat4750 describes and some flowered. I was hoping they would get bigger this year, but maybe from pat4750's experience they'll stay about the same size. Mine mainly got part/ afternoon sun.

I'm trying it for the first time this year, so we'll see.

Karen

It self sows here in zone 7a but not enough to be a nuisance. I love it's ferny foliage and the hummingbirds certainly love the flowers.
Alana

I've WS it the past two years, and it does bloom towards the end of the summer, but I agree that it would take a good sized clump to make a visual impact. It is worth growing though, especially if you are trying to attract hummingbirds. Hasn't resowed for me here in zone 5.

Bonnie

I winter-sowed this in 2009. Planted it in a little meadow area out back in part sun. I think it would have preferred full sun but I don't have much if any full sun on this lot. It also got munched on by the rabbit out there and was pretty stunted. Some sources say it's biennial, but mine bloomed the first year despite the rabbit munching. It is drought-tolerant and prefers good drainage.

Supposedly the hummers love it, but I have no idea if this is true, the meadow garden is too far back to watch. It didn't come back this year and I probably won't WS it again because I've got other hummingbird plants that are thriving and do well in partial sun (and no rabbit munching).

I grew this one year but it was in an area that I couldnt view easily so I dont know if hummers used much or at all. I cant imagine them not using it but it does tend to flower later in the season. This year I have pre-sprouted some seeds and am thinking of makign a special bed for them , maybe even a raised bed in full sun that will be of sandy loam with maybe some lime added in. The stems tend to be a bit willowy in the wind so I will support them with each other and a wire encasement such as is used for peonies. But this year they will be in an area so I can view them and I will know how much or how little hummers use them.