According to David Bradshaw from Ovum (in his paper on the subject published in October) ISV's are "likely to find that SaaS can produce considerable advantages.....not least reducing the buying cycle significantly. SaaS enables users to try the software before they buy it".
He also talks about the implications for Resellers too where "the biggest challenge will be the sales remuneration". How much do you pay your salesperson? Do you award £3k bonus for a contract worth £300k over three years or £1k bonus for £100k contract value in year one? Another issue is "how to transition from one [reward system] to the other".
He concludes by saying that any organisation getting involved in SaaS over the next year or so "should be ready for a period of uncertainty" though adds "not getting involved in SaaS would be an even greater risk". Very similar thinking to what IDC put in their recent paper.