I'm posting this abstract even though this med has not received much attention in the medical literature. However, the few articles I've seen the evaluations have been approving. It appears that Octreotide is worth keeping in mind as a secondary level abortive if the usual standard items have not been effective.
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Ann Neurol. 2004 Oct;56(4):488-94.

Subcutaneous Octreotide In Cluster Headache: Randomized Placebo-Controlled Double-Blind Crossover Study.
Matharu Ms, Levy Mj, Meeran K, Goadsby Pj.
Sourceheadache Group, Institute Of Neurology, Queen Square, London, United Kingdom.
Ann Neurol. 2004 Nov;56(5):751.

Abstract
Current Practical Evidence-Based Acute Treatments Of Cluster Headache Are Limited To Subcutaneous And Intranasal Formulations Of Sumatriptan, And Oxygen. Two Small Randomized, Double-Blind Trials Suggested Efficacy Of Somatostatin In Cluster Headache. We Sought To Determine Whether Octreotide, A Somatostatin Analog, Is Effective In The Abortive Treatment Of Acute Cluster Headache. Patients With Episodic And Chronic Cluster Headache, As Defined By The International Headache Society, Were Recruited To A Double-Blind Placebo-Controlled Crossover Study. Patients Were Instructed To Treat Two Attacks Of At Least Moderate Pain Severity, With At Least A 24-Hour Break, Using Subcutaneous Octreotide Microg Or Matching Placebo. The Primary End Point Was The Headache Response Defined As Very Severe, Severe, Or Moderate Pain Becomes Mild Or Nil, At 30 Minutes. The Primary End Point Was Examined Using A Multilevel Analysis Approach. A Total Of 57 Patients Were Recruited Of Whom 46 Provided Efficacy Data On Attacks Treated With Octreotide And 45 With Placebo. The Headache Response Rate With Subcutaneous Octreotide Was 52%, Whereas That With Placebo Was 36%. Modeling The Treatment Outcome As A Binomial Where Response Was Determined By Treatment, Using The Patient As The Level 2 Variable, And Considering Period Effect, Sex, And Cluster Headache Type As Other Variables Of Interest, We Found That The Effect Of Subcutaneous Octreotide 100 Microg Was Significantly Superior To Placebo (P < 0.01). SUBCUTANEOUS OCTREOTIDE 100 MICROG IS EFFECTIVE IN THE ACUTE TREATMENT OF CLUSTER HEADACHE WHEN COMPARED WITH PLACEBO.

Pmid:15455406[Pubmed]

I've never heard of this as you pointed out.  Sounds promising though.

I was looking into this drug a while back and found it very interesting.  I guess anything that will get rid of your cluster is interesting in itself, but what got me was that this is a somatostatin analog...And Somatostatin is also known as "growth hormone inhibiting-hormone"  So a drug that has as one of it's main actions lowering your growth hormone levels works for clusters...

And at least one of the Triptans (Zolmitriptan) has as one of it's actions INCREASED growth hormone.  Sounds like a pretty likely candidate for how triptans could be causing rebounds...but who knows, maybe it's just a coincidence.

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Anybody know anyone that's actually tried the Octreotide?