Now, the deal for Siebel makes a great deal of sense, unless you're worried about Oracle becoming more of a monopoly. The current market cap for Siebel is $5.39B, and they have $2.24B in cash on hand. They had revenue of $1.32B for the last year, and $883M in profit. This makes the $5.85B price Oracle agreed to fairly reasonable.
eBay is paying $2.6B for Skype, with another $1.5B offered for meeting financial targets. Skype seems to be a stretch for eBay because it doesn't seem to fall into the eBay business, but it could indicate a desire to move beyond just auctions. Skype isn't public, but some information was given out, they expect revenue of $60M this year, and $200M next year, but is not profitable. 54 million members, expected to double in a year, puts it at between $1-$2 dollars in revenue per user per yer, a very low number.
Now, Siebel is an older company, and its not going anywhere fast. Its been pretty flat for the last 2 years, and about equal to mid-99 before the bubble. Its a very obvious deal for Oracle and a fairly easy to understand price. Oracle is currently valued at $69B, has revenue of $11.8B and profit of $9.15B, so its about 10% of its value for about 10% more in income/profit, though I'm not sure how much of its own business would be cannibalized.
eBay is worth $53.1B and has $3.86B in revenue and $2.66B in profits. The only way this makes sense is if VOIP is on the verge of taking off, and Skype stands to be the largest player in the space... and that there is profit enough there in the business of undercutting the current telecoms. It seems like it may be a stretch to me. The potential is there... but its a risky move on eBay's part. No points for being risk averse, though.