My big disappointment was Mina lobata(Spanish Flag.) I knew it would bloom late so that wasn't the disappointment. It was that the blooms were so dinky after the wait! The leaves are attractive though.
Remy

Xeranthemum annuum was very disappointing! It's a pink flower for xeric conditions. They took a long time to start blooming. The plant is about 16" tall, the flower is small, it's a very pale pink, almost flesh-colored, and it really only opened part-way. It was pretty much an invisible plant! Do not be fooled by internet photos!

remy,
I grew spanish flags on my mailbox one year when I first started gardening...many years ago when the dinosaurs roamed the earth. They did very well for me. Guess because we have a long hot growing season.

stage-rat
I don't believe I've ever tried any of those.

Oh and let me add hosta tattoo to my "disappointment" list. I babied it several years as a tiny,tiny start a friend sent me,finally set it out this spring,it never got it's "tattoo" and the slugs and snails ADOORED it...yummy-yummy. Maybe next year,it'll come back and have a "tattoo".

Peggy

Spanish flags do great here due to the long warm growing season. I can see how they would disappoint in cooler zones.

My experience with xeranthemum annuum was very much like stage_rat's when using saved seeds- But if using commercial seeds, xeranthemum annuum DID look like the Internet photos: flat flowers with intense pink color. :)

I guess the 'intense pink' xeranthemum annuum is a commercial variety which always reverts back to a more boring pale pink wild-type if seeds are saved.

Nepeta nervosa "Blue Moon" has actually been impressive in my garden, and I plan on keeping it here! :)

Nemesias, including KLM, don't last long for me in my warm climate either.

I usually don't bother with Nemesias at all unless I can get a notably fragrant Nemesia, and even then I tend to keep it in a shaded windowox so it will last as long as it possibly can.

Some other 2009 flops:
'Spoon' currant tomato.
Could not hold a candle to the very flavorful local Hawaiian native tomato which is either called "sweet pea currant" or "menehune tomato" depending on the locality of the gardener.

'Spoon' was a less productive plant which yielded maybe 50 fruits vs the 100s of fruits from 'menehune'.'Spoon' also was fussier-needed more water and more pest control, only to still produce fruits with inferior flavor!

Sweet million and sweet 100 cherry tomato, and Gardeners Delight cherry: None of these cherries were as tasty, nor as reliably productive, as my old standby. They all suffered from disease in my garden and failed to yield well.

My old standby is the HI native cherry (Lycopersicon esculentum var. cerasiforme). It's possibly a variant or ancestor of 'Peacevine'.

my phacelia 'lavender lass', this was a commercial seed. Instead of lavender it was outright royal purple which would have been fine but not where I planted it and definitely not what I paid for, but thankful for my wintersown success I didn't feel like complaining. Also my tomatillo from another commercial company that turned out to be just unimpressive tomatoes.
I didn't mind non germination, or confusing descriptions from individual traders but I do expect that seed houses should get these things right. Perhaps, I'm being unreasonable, expecting even a company to be able to control the birds, bees, and wind. I guess if it happens again I'll just contact customer service and see about replacement or refund.

grovespirit,
my n. nervosa grew well...too darn well. The biggest disappointment was the color. Not the blue show in seed catalog.

shinyalloy,
my tomatillos and pumpkin on a stick didn't do well either. We had usually wet and cool year so that could have been the problem. I thought you could dry the pumpkins on a stick for floral arrangements but the few I did get did dry...they shriveled and got all "icky" looking.

Peggy

Sorry to hear that Peggy, I just added pumpkin on a stick to my wish list last week. Guess, I'll have to look it up and see if there is some trick to it, or whether it can be chalked up to your unusual weather. They always look so nifty in pictures.